Tagged Disease Rates

Many Children With MIS-C Had No Covid-19 Symptoms

Pediatricians should be vigilant, experts said, after the release of the largest U.S. study of the syndrome, MIS-C, that can strike young people weeks after their coronavirus infection.

Many children and teenagers who developed the mysterious inflammatory syndrome that can emerge several weeks after contracting the coronavirus never had classic Covid-19 symptoms at the time of their infection, according to the largest study so far of cases in the United States.

The study, led by researchers from the Centers for Disease Control and Prevention, found that in over 1,000 cases in which information about whether they got sick from their initial Covid-19 illness was available, 75 percent of the patients did not experience such symptoms. But two to five weeks later, they became sick enough to be hospitalized for the condition, called Multisystem Inflammatory Syndrome in Children (MIS-C), which can affect multiple organs, especially the heart.

Published Tuesday in JAMA Pediatrics, the study said that “most MIS-C illnesses are believed to result from asymptomatic or mild Covid-19” followed by a hyper-inflammatory response that appears to occur when the patients’ bodies have produced their maximum level of antibodies to the virus. Experts do not yet know why some young people, and a smaller number of adults, respond this way.

“It means primary-care pediatricians need to have a high index of suspicion for this because Covid is so prevalent in the society and children often have asymptomatic disease as their initial Covid infection,” said Dr. Jennifer Blumenthal, a pediatric intensivist and pediatric infectious disease specialist at Boston Children’s Hospital, who was not involved in the study.

The researchers evaluated 1,733 of the 2,090 cases of the syndrome in people age 20 and younger that had been reported to the C.D.C. as of January.

The findings show that although the syndrome is rare, it can be serious. The C.D.C’s data only included patients who were hospitalized. Over 90 percent of those young people experienced symptoms involving at least four organ systems and 58 percent needed treatment in intensive care units.

Many experienced significant heart issues: over half developed low blood pressure, 37 percent developed cardiogenic shock and 31 percent experienced cardiac dysfunction involving their heart’s inability to pump adequately. The study said that a significantly higher percentage of patients who had not had Covid-19 symptoms experienced those heart problems, compared with those who had initial coronavirus symptoms. A greater percentage of initially asymptomatic patients also ended up in intensive care.

“Even the kids with severe MIS-C, who were in the I.C.U. — the vast majority of them did not have a preceding illness that they recognized,” said Dr. Roberta DeBiasi, chief of infectious diseases at Children’s National Hospital in Washington, D.C., who was not involved in the research.

The study provided the most detailed demographic and geographic picture of the syndrome to date. About 34 percent of the patients were Black and 37 percent were Hispanic, reflecting the way that the coronavirus has disproportionately affected members of those communities. As the pandemic went on, the authors wrote, the proportion of patients who were white increased, comprising 20 percent of all cases. People of Asian heritage comprised just over 1 percent of patients.

Overall, nearly 58 percent of the patients were male, but the proportion was not the same across all ages. The youngest group — newborn to age 4 — had roughly equal numbers of boys and girls, and the male-to-female ratio increased in the older groups until it was more than two-to-one male to female in the 18-to-20 group.

The vast majority of patients (nearly 86 percent) were younger than 15. The study found that those under 5 had the lowest risk of serious heart complications and were less likely to need intensive care. Patients 10 and older were significantly more likely to develop issues like shock, low blood pressure and myocarditis (inflammation of the heart muscle).

“I think that’s similar to what we saw with Covid, that the older kids seemed to have more severe disease,” Dr. DeBiasi said. “And that’s because what makes people really sick from the Covid is the inflammatory aspect of it, so maybe these older kids, for whatever reasons, make more inflammation, whether that’s in primary Covid or MIS-C.”

Still, significant numbers of the youngest patients developed heart problems. In the newborn-to-4 age group, 36 percent had low blood pressure, 25 percent had shock and 44 percent were treated in the I.C.U.

Patients of all ages in the study had about the same occurrence of some of the less-common heart issues linked to the syndrome, including coronary aneurysms and fluid buildup. Children 14 and under were more likely to have rash and red eyes, while those older than 14 were more likely to have chest pain, shortness of breath and cough. Abdominal pain and vomiting afflicted about two-thirds of all patients.

There were 24 deaths recorded, spread across all age groups. There was no information in the study about whether patients had underlying medical conditions, but doctors and researchers have reported that young people with MIS-C were often previously healthy and significantly more likely to be healthy than the relatively small number of young people who become seriously ill from initial Covid infections.

Of the 1,075 patients for whom information about initial Covid illness was available, only 265 had symptoms at that time. They were more likely to be older — their median age was 11, while the median age of those with asymptomatic Covid infections was 8. But that could be because “younger children can’t express their concerns as well,” said Dr. Blumenthal, who co-wrote an editorial about the study.

“We don’t necessarily know if there’s actually less symptomatology in the very young population, ” she said.

Similarly unclear are the reasons behind the study’s finding that in the first wave of MIS-C, from March 1 to July 1, 2020, young people were more prone to a few of the most serious heart complications. Dr. DeBiasi said that did not match the experience of her hospital, where “the kids were sicker in the second wave.”

The study documented two waves of MIS-C cases that followed surges in overall coronavirus cases by about a month or more. “The most recent third peak of the Covid-19 pandemic appears to be leading to another MIS-C peak perhaps involving urban and rural communities,” the authors wrote.

The study found that most of the states where the rate of MIS-C cases per population was highest were in the Northeast, which had the first surge of cases, and the South. By contrast, most states with high per-population rates of children with Covid-19 but low rates of MIS-C were in the Midwest and West. While the concentration of cases spread from large cities to smaller towns over time, it wasn’t as pronounced as the overall pandemic trends, the authors said.

Dr. Blumenthal said that geographic pattern could reflect that the “understanding of the complications of the disease” hadn’t caught up to its prevalence in different regions or that many states with lower rates of MIS-C have less ethnically diverse populations. “It could also be something about Covid itself, although we don’t know that,” she said. “Right now, we don’t know anything about how the variants necessarily affect children.”

The study represented only the strictest criteria for MIS-C, excluding about 350 reported cases that met the C.D.C. definition of the syndrome but had a negative antibody test or primarily involved respiratory symptoms. Dr. DeBiasi said there are also many probable MIS-C cases that are not reported to the C.D.C. because they don’t meet all the official criteria.

“These probable MIS-C kids, in real life that’s a big chunk of kids,” she said. In addition, while the focus so far has been on serious cases, “there’s another whole group of kids that may actually have mild MIS-C.”

If a community has experienced a recent coronavirus surge, then “just because the kid says, ‘I never had Covid or my parents never had it,’ that doesn’t mean the kid in front of you doesn’t have MIS-C,” Dr. DeBiasi said. “If your city has Covid, then get ready.”

Many Children With Serious Inflammatory Syndrome Had No Covid Symptoms

Pediatricians should be vigilant, experts said, after the release of the largest U.S. study of the syndrome, MIS-C, that can strike young people weeks after their coronavirus infection.

Many children and teenagers who developed the mysterious inflammatory syndrome that can emerge several weeks after contracting the coronavirus never had classic Covid-19 symptoms at the time of their infection, according to the largest study so far of cases in the United States.

The study, led by researchers from the Centers for Disease Control and Prevention, found that in over 1,000 cases in which information about whether they got sick from their initial Covid-19 illness was available, 75 percent of the patients did not experience such symptoms. But two to five weeks later, they became sick enough to be hospitalized for the condition, called Multisystem Inflammatory Syndrome in Children (MIS-C), which can affect multiple organs, especially the heart.

Published Tuesday in JAMA Pediatrics, the study said that “most MIS-C illnesses are believed to result from asymptomatic or mild Covid-19” followed by a hyper-inflammatory response that appears to occur when the patients’ bodies have produced their maximum level of antibodies to the virus. Experts do not yet know why some young people, and a smaller number of adults, respond this way.

“It means primary-care pediatricians need to have a high index of suspicion for this because Covid is so prevalent in the society and children often have asymptomatic disease as their initial Covid infection,” said Dr. Jennifer Blumenthal, a pediatric intensivist and pediatric infectious disease specialist at Boston Children’s Hospital, who was not involved in the study.

The researchers evaluated 1,733 of the 2,090 cases of the syndrome in people age 20 and younger that had been reported to the C.D.C. as of January.

The findings show that although the syndrome is rare, it can be serious. The C.D.C’s data only included patients who were hospitalized. Over 90 percent of those young people experienced symptoms involving at least four organ systems and 58 percent needed treatment in intensive care units.

Many experienced significant heart issues: over half developed low blood pressure, 37 percent developed cardiogenic shock and 31 percent experienced cardiac dysfunction involving their heart’s inability to pump adequately. The study said that a significantly higher percentage of patients who had not had Covid-19 symptoms experienced those heart problems, compared with those who had initial coronavirus symptoms. A greater percentage of initially asymptomatic patients also ended up in intensive care.

“Even the kids with severe MIS-C, who were in the I.C.U. — the vast majority of them did not have a preceding illness that they recognized,” said Dr. Roberta DeBiasi, chief of infectious diseases at Children’s National Hospital in Washington, D.C., who was not involved in the research.

The study provided the most detailed demographic and geographic picture of the syndrome to date. About 34 percent of the patients were Black and 37 percent were Hispanic, reflecting the way that the coronavirus has disproportionately affected members of those communities. As the pandemic went on, the authors wrote, the proportion of patients who were white increased, comprising 20 percent of all cases. People of Asian heritage comprised just over 1 percent of patients.

Overall, nearly 58 percent of the patients were male, but the proportion was not the same across all ages. The youngest group — newborn to age 4 — had roughly equal numbers of boys and girls, and the male-to-female ratio increased in the older groups until it was more than two-to-one male to female in the 18-to-20 group.

The vast majority of patients (nearly 86 percent) were younger than 15. The study found that those under 5 had the lowest risk of serious heart complications and were less likely to need intensive care. Patients 10 and older were significantly more likely to develop issues like shock, low blood pressure and myocarditis (inflammation of the heart muscle).

“I think that’s similar to what we saw with Covid, that the older kids seemed to have more severe disease,” Dr. DeBiasi said. “And that’s because what makes people really sick from the Covid is the inflammatory aspect of it, so maybe these older kids, for whatever reasons, make more inflammation, whether that’s in primary Covid or MIS-C.”

Still, significant numbers of the youngest patients developed heart problems. In the newborn-to-4 age group, 36 percent had low blood pressure, 25 percent had shock and 44 percent were treated in the I.C.U.

Patients of all ages in the study had about the same occurrence of some of the less-common heart issues linked to the syndrome, including coronary aneurysms and fluid buildup. Children 14 and under were more likely to have rash and red eyes, while those older than 14 were more likely to have chest pain, shortness of breath and cough. Abdominal pain and vomiting afflicted about two-thirds of all patients.

There were 24 deaths recorded, spread across all age groups. There was no information in the study about whether patients had underlying medical conditions, but doctors and researchers have reported that young people with MIS-C were often previously healthy and significantly more likely to be healthy than the relatively small number of young people who become seriously ill from initial Covid infections.

Of the 1,075 patients for whom information about initial Covid illness was available, only 265 had symptoms at that time. They were more likely to be older — their median age was 11, while the median age of those with asymptomatic Covid infections was 8. But that could be because “younger children can’t express their concerns as well,” said Dr. Blumenthal, who co-wrote an editorial about the study.

“We don’t necessarily know if there’s actually less symptomatology in the very young population, ” she said.

Similarly unclear are the reasons behind the study’s finding that in the first wave of MIS-C, from March 1 to July 1, 2020, young people were more prone to a few of the most serious heart complications. Dr. DeBiasi said that did not match the experience of her hospital, where “the kids were sicker in the second wave.”

The study documented two waves of MIS-C cases that followed surges in overall coronavirus cases by about a month or more. “The most recent third peak of the Covid-19 pandemic appears to be leading to another MIS-C peak perhaps involving urban and rural communities,” the authors wrote.

The study found that most of the states where the rate of MIS-C cases per population was highest were in the Northeast, which had the first surge of cases, and the South. By contrast, most states with high per-population rates of children with Covid-19 but low rates of MIS-C were in the Midwest and West. While the concentration of cases spread from large cities to smaller towns over time, it wasn’t as pronounced as the overall pandemic trends, the authors said.

Dr. Blumenthal said that geographic pattern could reflect that the “understanding of the complications of the disease” hadn’t caught up to its prevalence in different regions or that many states with lower rates of MIS-C have less ethnically diverse populations. “It could also be something about Covid itself, although we don’t know that,” she said. “Right now, we don’t know anything about how the variants necessarily affect children.”

The study represented only the strictest criteria for MIS-C, excluding about 350 reported cases that met the C.D.C. definition of the syndrome but had a negative antibody test or primarily involved respiratory symptoms. Dr. DeBiasi said there are also many probable MIS-C cases that are not reported to the C.D.C. because they don’t meet all the official criteria.

“These probable MIS-C kids, in real life that’s a big chunk of kids,” she said. In addition, while the focus so far has been on serious cases, “there’s another whole group of kids that may actually have mild MIS-C.”

If a community has experienced a recent coronavirus surge, then “just because the kid says, ‘I never had Covid or my parents never had it,’ that doesn’t mean the kid in front of you doesn’t have MIS-C,” Dr. DeBiasi said. “If your city has Covid, then get ready.”

Can Vaccinated People Spread the Virus? We Don’t Know, Scientists Say.

Researchers pushed back after the C.D.C. director asserted that vaccinated people “do not carry the virus.”

The Centers for Disease Control and Prevention on Thursday walked back controversial comments made by its director, Dr. Rochelle P. Walensky, suggesting that people who are vaccinated against the coronavirus never become infected or transmit the virus to others.

The assertion called into question the precautions that the agency had urged vaccinated people to take just last month, like wearing masks and gathering only under limited circumstances with unvaccinated people.

“Dr. Walensky spoke broadly during this interview,” an agency spokesman told The Times. “It’s possible that some people who are fully vaccinated could get Covid-19. The evidence isn’t clear whether they can spread the virus to others. We are continuing to evaluate the evidence.”

The agency was responding in part to criticism from scientists who noted that current research was far from sufficient to claim that vaccinated people cannot spread the virus.

The data suggest that “it’s much harder for vaccinated people to get infected, but don’t think for one second that they cannot get infected,” said Paul Duprex, director of the Center for Vaccine Research at the University of Pittsburgh.

In a television interview with MSNBC’s Rachel Maddow, Dr. Walensky referred to data published by the C.D.C. showing that one dose of the Moderna or Pfizer-BioNTech vaccine was 80 percent effective at preventing infection, and two doses were 90 percent effective.

That certainly suggested that transmission from vaccinated people might be unlikely, but Dr. Walensky’s comments hinted that protection was complete. “Our data from the C.D.C. today suggests that vaccinated people do not carry the virus, don’t get sick,” she said. “And that it’s not just in the clinical trials, it’s also in real-world data.”

Dr. Walensky went on to emphasize the importance of continuing to wear masks and maintain precautions, even for vaccinated people. Still, the brief comment was widely interpreted as saying that the vaccines offered complete protection against infection or transmission.

In a pandemic that regularly spawns scientific misunderstanding, experts said they were sympathetic to Dr. Walensky and her obvious desire for Americans to continue to take precautions. It was only Monday that she said rising caseloads had left her with a sense of “impending doom.”

“If Dr. Walensky had said most vaccinated people do not carry virus, we would not be having this discussion,” said John Moore, a virologist at Weill Cornell Medicine in New York.

“What we know is the vaccines are very substantially effective against infection — there’s more and more data on that — but nothing is 100 percent,” he added. “It is an important public health message that needs to be gotten right.”

Misinterpretation could disrupt the agency’s urgent pleas for immunization, some experts said. As of Wednesday, 30 percent of Americans had received at least one dose of a vaccine and 17 percent were fully immunized.

“There cannot be any daylight between what the research shows — really impressive but incomplete protection — and how it is described,” said Dr. Peter Bach, director of the Center for Health Policy and Outcomes at Memorial Sloan Kettering Cancer Center in New York.

“This opens the door to the skeptics who think the government is sugarcoating the science,” Dr. Bach said, “and completely undermines any remaining argument why people should keep wearing masks after being vaccinated.”

All of the coronavirus vaccines are spectacularly successful at preventing serious disease and death from Covid-19, but how well they prevent infection has been less clear.

Clinical trials of the vaccines were designed only to assess whether the vaccines prevent serious illness and death. The research from the C.D.C. on Monday brought the welcome conclusion that the vaccines are also extremely effective at preventing infection.

The study enrolled 3,950 health care workers, emergency responders and others at high risk of infection. The participants swabbed their noses each week and sent the samples in for testing, which allowed federal researchers to track all infections, symptomatic or not. Two weeks after vaccination, the vast majority of vaccinated people remained virus-free, the study found.

Follow-up data from clinical trials support that finding. In results released by Pfizer and BioNTech on Wednesday, for example, 77 people who received the vaccine had a coronavirus infection, compared with 850 people who got a placebo.

“Clearly, some vaccinated people do get infected,” Dr. Duprex said. “We’re stopping symptoms, we’re keeping people out of hospitals. But we’re not making them completely resistant to an infection.”

The number of vaccinated people who become infected is likely to be higher among those receiving vaccines made by Johnson & Johnson and AstraZeneca, which have a lower efficacy, experts said. (Still, those vaccines are worth taking, because they uniformly prevent serious illness and death.)

Infection rates may also be higher among people exposed to a virus variant that can sidestep the immune system.

Cases across the country are once again on the upswing, threatening a new surge. Dr. Walensky’s comment came just a day after she made an emotional appeal to the American public to continue taking precautions.

“I am asking you to just hold on a little longer, to get vaccinated when you can, so that all of those people that we all love will still be here when this pandemic ends,” she said.

Given the rising numbers, it’s especially important that immunized people continue to protect those who have not yet been immunized against the virus, experts said.

“Vaccinated people should not be throwing away their masks at this point,” Dr. Moore said. “This pandemic is not over.”

Virus Variants Can Infect Mice, Scientists Report

Infected rodents pose no immediate danger to humans, but the research suggests that mutations are helping the coronavirus expand its range of potential hosts.

Bats, humans, monkeys, minks, big cats and big apes — the coronavirus can make a home in many different animals. But now the list of potential hosts has expanded to include mice, according to an unnerving new study.

Infected rodents pose no immediate risk to people, even in cities like London and New York, where they are ubiquitous and unwelcome occupants of subway stations, basements and backyards.

Still, the finding is worrying. Along with previous work, it suggests that new mutations are giving the virus the ability to replicate in a wider array of animal species, experts said.

“The virus is changing, and unfortunately it’s changing pretty fast,” said Timothy Sheahan, a virologist at the University of North Carolina at Chapel Hill, who was not involved in the new study.

In the study, the researchers introduced the virus into the nasal passages of laboratory mice. The form of the virus first identified in Wuhan, China, cannot infect laboratory mice, nor can B.1.1.7, a variant that has been spreading across much of Europe, the researchers found.

But B.1.351 and P1, the variants discovered in South Africa and Brazil, can replicate in rodents, said Dr. Xavier Montagutelli, a veterinarian and mouse geneticist at the Pasteur Institute in Paris, who led the study. The research, posted online earlier this month, has not yet been reviewed for publication in a scientific journal.

The results indicate only that infection in mice is possible, Dr. Montagutelli said. Mice caught in the wild have not been found to be infected with the coronavirus, and so far, the virus does not seem to be able to jump from humans to mice, from mice to humans, or from mice to mice.

“What our results emphasize is that it is necessary to regularly assess the range of species that the virus can infect, especially with the emergence of new variants,” Dr. Montagutelli said.

The coronavirus is thought to have emerged from bats, with perhaps another animal acting as an intermediate host, and scientists worry that the virus may return to what they describe as an animal “reservoir.”

Apart from potentially devastating those animal populations, a coronavirus spreading in another species may then acquire dangerous mutations, returning to humans in a form the current vaccines weren’t designed to fend off.

A mink looks out from its cage at a farm in Denmark, where mink populations were hit hard by the coronavirus.
A mink looks out from its cage at a farm in Denmark, where mink populations were hit hard by the coronavirus.Mads Claus Rasmussen/Agence France-Presse — Getty Images

Minks are the only animals known to be able to catch the coronavirus from humans and pass it back. In early November, Denmark culled 17 million farmed mink to prevent the virus from evolving into dangerous new variants in the animals.

More recently, researchers found that B.1.1.7 infections in domesticated cats and dogs can cause the pets to develop heart problems similar to those seen in people with Covid-19.

To establish a successful infection, the coronavirus must bind to a protein on the surface of animal cells, gain entry into the cells, and exploit their machinery to make copies of itself. The virus must also evade the immune system’s early attempts at thwarting the infection.

Given all those requirements, it is “quite extraordinary” that the coronavirus can infect so many species, said Vincent Munster, a virologist at the National Institute of Allergy and Infectious Diseases. “Typically, viruses have a more curtailed host range.”

Mice are a known reservoir for hantavirus, which causes a rare and deadly disease in people. Even though the coronavirus variants don’t seem to be able to jump from mice to people, there is potential for them to spread among rodents, evolve into new variants, and then infect people again, Dr. Munster said.

The variants may also threaten endangered species like black-footed ferrets. “This virus seems to be able to surprise us more than anything else, or any other previous virus,” Dr. Munster said. “We have to err on the side of caution.”

Dr. Sheahan said he was more concerned about transmission to people from farm animals and pets than from mice.

“You’re not catching wild mice in your house and snuggling — getting all up in their face and sharing the same airspace, like maybe with your cat or your dog,” he said. “I’d be more worried about wild or domestic animals with which we have a more intimate relationship.”

But he and other experts said the results emphasized the need to closely monitor the rapid changes in the virus.

“It’s like a moving target — it’s crazy,” he added. “There’s nothing we can do about it, other than try and get people vaccinated really fast.”

The Pfizer-BioNTech Vaccine Is Said to Be Powerfully Protective in Adolescents

A clinical trial found no infections among vaccinated children ages 12 to 15, the companies said, and there were no serious side effects. The data have not yet been reviewed by independent experts.

The Pfizer-BioNTech coronavirus vaccine is extremely effective in adolescents 12 to 15 years old, perhaps even more so than in adults, the companies reported on Wednesday. No infections were found among children who received the vaccine in a recent clinical trial, the drug makers said; the children produced strong antibody responses and experienced no serious side effects.

The findings, if they hold up, may speed a return to normalcy for millions of American families. Depending on regulatory approval, vaccinations could begin before the start of the next academic year for middle school and high school students, and for elementary school children not long after.

The companies announced the results in a news release that did not include detailed data from the trial, which has not yet been peer-reviewed nor published in a scientific journal. Still, the news drew praise and excitement from experts.

“Oh my god, I’m so happy to see this — this is amazing,” said Akiko Iwasaki, an immunologist at Yale University. If the vaccines’s performance in adults was A-plus, the results in children were “A-plus-plus.”

The good news arrives even as the country records another rise in infections and health officials renew calls for Americans to heed precautions and get vaccinated. On Monday, Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, said that rising cases had left her with sense of “impending doom,” while President Biden called on state and local officials to reinstate mask mandates.

Vaccination efforts are accelerating throughout the nation. As of Tuesday, 29 percent of adults had received at least one dose of a coronavirus vaccine, and 16 percent had been fully inoculated, according to the C.D.C.

But the country cannot hope to reach herd immunity — the point at which immunity becomes so widespread that the coronavirus slows its crawl through the population — without also inoculating the youngest Americans, some experts say. Children under 18 account for about 23 percent of the population in the United States.

“The sooner that we can get vaccines into as many people as possible, regardless of their age, the sooner we will be able to really feel like we’re ending this pandemic for good,” said Angela Rasmussen, a virologist affiliated with Georgetown University in Washington.

Data from Israel suggest that vaccinating adults alone can significantly decrease the number of cases, but “long term, to hit the herd immunity threshold, we will have to vaccinate children,” she said.

The trial included 2,260 adolescents ages 12 to 15. The children received two doses of the vaccine three weeks apart — the same amounts and schedule used for adults — or a placebo of saltwater.

The researchers recorded 18 cases of coronavirus infection in the placebo group, and none among the children who received the vaccine. Still, the low number of infections makes it difficult to be too specific about the vaccine’s efficacy in the population at large, Dr. Rasmussen said.

“But obviously, it looks good for the vaccine if there were zero Covid cases among the vaccinated people,” she added.

The adolescents who got the vaccine produced much higher levels of antibodies on average, compared with participants 16 to 25 years of age in an earlier trial. The children experienced the same minor side effects as older participants, although the companies declined to be more specific.

Dr. Iwasaki said she had expected antibody levels in adolescents to be comparable to those in young adults. “But they’re getting even better levels from the vaccines,” she said. “That’s really incredible.”

She and other experts cautioned that the vaccine might be less effective in children, and adults, against some of the variants that have begun circulating in the United States.

Pfizer and BioNTech have begun a clinical trial of the vaccine in children under 12 and started inoculations of children ages 5 to 11 just last week. Company scientists plan to start testing the vaccine next week in even younger children, ages 2 to 5, followed by trials in children ages 6 months to 2 years.

Results from that three-phase trial are expected in the second half of the year, and the companies hope to make the vaccine available for children under 12 early next year.

“We share the urgency to expand the use of our vaccine to additional populations and are encouraged by the clinical trial data from adolescents between the ages of 12 and 15,” Albert Bourla, Pfizer’s chairman and chief executive officer, said in a statement.

Moderna has also been testing its vaccine in children. Results from a trial in adolescents ages 12 to 17 are expected in the next few weeks and in children 6 months to 12 years old in the second half of this year.

AstraZeneca started testing its vaccine in children 6 months and older last month, and Johnson & Johnson has said it will wait for results from trials in older children before testing its vaccine in children under 12.

Some parents have said they are reluctant to immunize their children because the risk posed by the virus is low. Children make up fewer than 1 percent of deaths from Covid-19, but about 2 percent of children who get the illness require hospital care.

The new results may not sway all of those parents, but they may reassure parents who have been wary of the vaccines, said Jennifer Nuzzo, an epidemiologist at the Johns Hopkins Center for Health Security.

“While I don’t think we have to wait until children are vaccinated to fully reopen schools, being able to vaccinate children may help some families feel safer about returning to school,” she said.

Pfizer and BioNTech plan to request from the Food and Drug Administration an amendment to the emergency use authorization for their vaccine, in hopes of beginning immunizations of older children before the start of the next school year. The companies also are planning to submit their data for peer review and publication in a scientific journal.

They will monitor the participants for two years after the second dose to assess the vaccine’s long-term safety and efficacy. Side effects of vaccines are usually apparent within the first six weeks, said Dr. Kristin Oliver, a pediatrician and vaccine expert at Mount Sinai Hospital in New York. “Still, it’s good to know that safety monitoring is going to continue,” she said.

The C.D.C. recommends that people avoid getting other vaccines for two weeks before and after receiving the two doses of the coronavirus vaccine.

But children receive more vaccines in the few weeks before the school year than at any other time, Dr. Oliver noted, so pediatricians and parents should aim to get those other immunizations done earlier than usual.

The coronavirus vaccines should ideally be given by pediatricians who have deep experience in immunizing children, Dr. Oliver added. “Now is the time to start planning how that rollout is going to take place in this age group,” she said.

Pfizer Begins Testing Its Vaccine in Young Children

Other drug makers have begun similar trials of their Covid-19 vaccines. If they work in children younger than 12 as expected, it will be easier for the U.S. to reach herd immunity.

Pfizer has begun testing its Covid-19 vaccine in children under 12, a significant step in turning back the pandemic. The trial’s first participants, a pair of 9-year-old twin girls, were immunized at Duke University in North Carolina on Wednesday.

Results from the trial are expected in the second half of the year, and the company hopes to vaccinate younger children early next year, said Sharon Castillo, a spokeswoman for the pharmaceutical company.

Moderna also is beginning a trial of its vaccine in children six months to 12 years of age. Both companies have been testing their vaccines in children 12 and older, and expect those results in the next few weeks.

AstraZeneca last month began testing its vaccine in children six months and older, and Johnson & Johnson has said it plans to extend trials of its vaccine to young children after assessing its performance in older children.

Immunizing children will help schools to reopen as well as help to end the pandemic, said Dr. Emily Erbelding, an infectious diseases physician at the National Institutes of Health who oversees testing of Covid-19 vaccines in special populations.

An estimated 80 percent of the population may need to be vaccinated for the United States to reach herd immunity, the threshold at which the coronavirus runs out of people to infect. Some adults may refuse to be vaccinated, and others may not produce a robust immune response.

Children under 18 account for about 23 percent of the population in the United States, so even if a vast majority of adults opt for vaccines, “herd immunity might be hard to achieve without children being vaccinated,” Dr. Erbelding said.

Pfizer had initially said it would wait for data from older children before starting trials of its vaccine in children under 12. But “we were encouraged by the data from the 12 to 15 group,” said Ms. Castillo, who did not elaborate on the results so far.

Scientists will test three doses of the Pfizer vaccine — 10, 20 and 30 micrograms — in 144 children. Each dose will be assessed first in children 5 through 11 years of age, then in children ages 2 through 4 years, and finally in the youngest group, six months to 2 years.

After determining the most effective dose, the company will test the vaccine in 4,500 children. About two-thirds of the participants will be randomly selected to receive two doses 21 days apart; the remaining will get two placebo shots of saline. The researchers will assess the children’s immune response in blood drawn seven days after the second dose.

“It sounds like a good plan, and it’s exciting that another Covid-19 vaccine is moving forward with trials in children,” said Dr. Kristin Oliver, a pediatrician and vaccine expert at Mount Sinai Hospital in New York.

Dr. Oliver said about half of the parents she sees in practice are eagerly waiting for vaccines, and even to volunteer their children for clinical trials, while the rest are skeptical because comparatively few children become seriously ill from coronavirus infection.

Both groups of parents will benefit from knowing exactly how safe and effective the vaccines are in children, she said.

Children represent 13 percent of all reported cases in the United States. More than 3.3 million children have tested positive for the virus, at least 13,000 have been hospitalized and at least 260 have died, noted Dr. Yvonne Maldonado, who represents the American Academy of Pediatrics on the federal Advisory Committee on Immunization Practices.

The figures do not fully capture the damage to children’s health. “We don’t know what the long-term effects of Covid infection are going to be,” Dr. Maldonado said.

Other vaccines have helped to control many horrific childhood diseases that can cause long-term complications, she added: “For some of us who’ve seen that, we don’t want to go back to those days.”

Children often react more strongly to vaccines than adults do, and infants and toddlers in particular can experience high fevers. Any side effects are likely to appear soon after the shot, within the first week and certainly within the first few weeks, experts have said.

Some vaccines are tested only in animals before being assessed in children, and have to be monitored carefully for side effects.

“But this is a little different, because we’ve already had experience with tens of millions of people with these vaccines,” Dr. Maldonado said. “So there’s a higher degree of confidence now in giving this vaccine to kids.”

Some experts suggested that the Food and Drug Administration may require up to six months of safety data from studies of children before authorizing the Covid-19 vaccines. But a spokeswoman said the agency did not expect six months of safety data to support the vaccines’ authorization.

The Pfizer-BioNTech vaccine is authorized for children 16 through 18 years old, and the authorization for that age group was based on just two months of safety data, she said.

Parents will want to know how the companies and the F.D.A. plan to monitor and disclose side effects from the vaccines, and how long they will continue to follow trial participants after the vaccines’ authorization, Dr. Oliver said.

“I think everyone has learned throughout this,” she said. “The more transparent you can be, the better.”

Why It Pays to Think Outside the Box on Coronavirus Tests

Universities and other institutions looking to protect themselves from Covid-19 may benefit from sharing their testing resources with the wider community, a new study suggests.

Last year, when the National Football League decided to stage its season in the midst of the coronavirus pandemic, it went all-in on testing. The league tested all players and personnel before they reported for summer training camp, and continued near-daily testing in the months that followed. Between Aug. 1 and the Super Bowl in early February, the N.F.L. administered almost one million tests to players and staff.

Many other organizations have sought safety in mass testing. The University of Illinois is testing its students, faculty and staff twice a week and has conducted more than 1.6 million tests since July. Major corporations, from Amazon to Tyson Foods, have rolled out extensive testing programs for their own employees.

Now, a new analysis suggests that schools, businesses and other organizations that want to keep themselves safe should think beyond strictly themselves. By dedicating a substantial proportion of their tests to people in the surrounding community, institutions could reduce the number of Covid-19 cases among their members by as much as 25 percent, researchers report in a new paper, which has not yet been published in a scientific journal.

“It’s natural in an outbreak for people to become self-serving, self-focused,” said Dr. Pardis Sabeti, a computational biologist at Harvard University and the Broad Institute who lead the analysis. But, she added, “If you’ve been in enough outbreaks you just understand that testing in a box doesn’t makes sense. These things are communicable, and they’re coming in from the community.”

The study has “really profound implications, especially if others can replicate it, said David O’Connor, a virologist at the University of Wisconsin, Madison, who was not involved in the analysis but reviewed a draft of the paper. As the pandemic enters its second year, he said, “We want to start using more sophisticated modeling and probably economic theory to inform what an optimal testing program would look like.”

Dr. Sabeti is an epidemic veteran, part of teams that responded to an Ebola outbreak in West Africa in 2014 and a mumps outbreak in the Boston area a few years later. When the coronavirus closed down the country last spring, many colleges and universities sought her advice on how to safely reopen.

At a time when testing resources were in short supply, many of these institutions were proposing intensive, expensive testing regimens focused entirely on their own members. Again and again, Dr. Sabeti suggested that universities think more broadly, and allocate some of their tests to people who might be friends, family members or neighbors of their students and employees.

“The metaphor I often used on the calls was to say, ‘You’re in a drought in a place with a lot of forest fires, and you have a shortage of fire alarms,’” she recalled. “‘And if you run out and buy every fire alarm and install it in your own house, you’ll be able to pick up a fire the moment it hits your house, but at that point it’s burning to the ground.’”

Still, convincing university officials to divert precious testing resources away from their own institutions was a hard sell, Dr. Sabeti said, especially without data on the effectiveness of the approach. So she and her colleagues decided to gather some.

“Fundamentally, the paper is about the intersection of kindness and success — how being generous with one’s resources actually is the most effective” strategy, said one of the study’s authors.
“Fundamentally, the paper is about the intersection of kindness and success — how being generous with one’s resources actually is the most effective” strategy, said one of the study’s authors.Pete Kiehart for The New York Times

They developed an epidemiological model to simulate how a virus might spread through a midsize university, like Colorado Mesa University, one of the schools Dr. Sabeti’s team has been advising. (Several C.M.U. officials and researchers are co-authors of the paper.)

Using real-world data from C.M.U., the researchers created a baseline scenario in which 1 percent of people at the school, and 6 percent of those in the surrounding county, were infected by the coronavirus, and the university was testing 12 percent of its members every day. The team assumed that they had a complete list of each university member’s close off-campus contacts, and that if someone tested positive for the virus, they and their contacts would quarantine until they were no longer infectious.

Under these conditions, the researchers found, if the university used all of its tests on its own members, it would have roughly 200 Covid-19 cases after 40 days. But if instead it parceled out some of those tests, using them on community members who were close contacts of students and staff, the number of cases dropped by one-quarter.

“The optimal proportion of tests to use outside the institution on those targeted, first-degree contacts came out to be about 45 percent,” said Ivan Specht, an undergraduate researcher in Dr. Sabeti’s lab and a co-author of the paper. In short, institutions could reduce their caseloads by one-fourth if they used almost half their tests on people just outside their direct membership. That percentage “is remarkably high considering that most institutions use zero percent of their tests outside of themselves,” Mr. Specht noted.

The researchers then tweaked the model’s parameters in various ways: What if the virus were more prevalent? What if students and staff did not report all their contacts? What if they were better about mask-wearing and social distancing? What if the university deployed more tests, or fewer?

Unsurprisingly, the more testing the university did, and the more information it had about its members’ close contacts, the fewer Covid-19 cases there were. But in virtually every scenario, sharing at least some tests with the broader community led to fewer cases than hoarding them.

“The surprising thing is just how robust that finding is in the face of some pretty plausible variations,” said A. David Paltiel, a professor of health policy and management at Yale School of Public Health, who was not involved in the study.

Still, he noted, there were plenty of scenarios that the model didn’t test, and the paper still needs to undergo a thorough peer review.

Its predictions should also be tested in the real world, Dr. O’Connor said: “It needs to be explored and tested head-to-head with other allocation methods.”

But if the findings hold up, it would suggest that schools and other institutions that are trying to reopen safely should think beyond their own walls when they develop testing programs. “Even if your goal is only to protect the students in your care, you will still be doing the maximum to protect those students by taking care of the people in the surrounding community,” Dr. Paltiel said. “That’s a pretty strong argument.”

Some universities are beginning to adopt this outlook. C.M.U. now offers free tests to all of its students’ self-reported contacts, whether or not they are affiliated with the university, and runs a testing site that is open to local residents, said Amy Bronson, a co-chair of the university’s Covid-19 task force and an author of the paper.

And in November, the University of California, Davis, began offering free coronavirus tests to anyone who lives or works in the city. The Healthy Davis Together program, a partnership with the city, has since administered more than 450,000 tests and identified more than 1,000 people with the virus, said Brad Pollock, an epidemiologist at U.C. Davis who directs the project.

“A virus does not respect geographic boundaries,” Dr. Pollock said. “It is ludicrous to think that you can get control of an acute infectious respiratory disease like Covid-19, in a city like Davis that hosts a very large university, without coordinated public health measures that connect both the university and the community.”

There are barriers to the more altruistic approach, including internal political pressure to use testing resources in house and concerns about legal liability. But the researchers hope that their model convinces at least some institutions to rethink their strategy, not only during this epidemic but also in future ones.

“An outbreak is an opportunity to buy a lot of community good will, or to burn a lot of community good will,” Dr. Sabeti said. “We could have spent an entire year building up that relationship between organizations and institutions and their communities. And we would have done all that hard work together, as opposed to everybody turning inward.”

Why It Pays to Think Outside the Box on Coronavirus Tests

Universities and other institutions looking to protect themselves from Covid-19 may benefit from sharing their testing resources with the wider community, a new study suggests.

Last year, when the National Football League decided to stage its season in the midst of the coronavirus pandemic, it went all-in on testing. The league tested all players and personnel before they reported for summer training camp, and continued near-daily testing in the months that followed. Between Aug. 1 and the Super Bowl in early February, the N.F.L. administered almost one million tests to players and staff.

Many other organizations have sought safety in mass testing. The University of Illinois is testing its students, faculty and staff twice a week and has conducted more than 1.6 million tests since July. Major corporations, from Amazon to Tyson Foods, have rolled out extensive testing programs for their own employees.

Now, a new analysis suggests that schools, businesses and other organizations that want to keep themselves safe should think beyond strictly themselves. By dedicating a substantial proportion of their tests to people in the surrounding community, institutions could reduce the number of Covid-19 cases among their members by as much as 25 percent, researchers report in a new paper, which has not yet been published in a scientific journal.

“It’s natural in an outbreak for people to become self-serving, self-focused,” said Dr. Pardis Sabeti, a computational biologist at Harvard University and the Broad Institute who lead the analysis. But, she added, “If you’ve been in enough outbreaks you just understand that testing in a box doesn’t makes sense. These things are communicable, and they’re coming in from the community.”

The study has “really profound implications, especially if others can replicate it, said David O’Connor, a virologist at the University of Wisconsin, Madison, who was not involved in the analysis but reviewed a draft of the paper. As the pandemic enters its second year, he said, “We want to start using more sophisticated modeling and probably economic theory to inform what an optimal testing program would look like.”

Dr. Sabeti is an epidemic veteran, part of teams that responded to an Ebola outbreak in West Africa in 2014 and a mumps outbreak in the Boston area a few years later. When the coronavirus closed down the country last spring, many colleges and universities sought her advice on how to safely reopen.

At a time when testing resources were in short supply, many of these institutions were proposing intensive, expensive testing regimens focused entirely on their own members. Again and again, Dr. Sabeti suggested that universities think more broadly, and allocate some of their tests to people who might be friends, family members or neighbors of their students and employees.

“The metaphor I often used on the calls was to say, ‘You’re in a drought in a place with a lot of forest fires, and you have a shortage of fire alarms,’” she recalled. “‘And if you run out and buy every fire alarm and install it in your own house, you’ll be able to pick up a fire the moment it hits your house, but at that point it’s burning to the ground.’”

Still, convincing university officials to divert precious testing resources away from their own institutions was a hard sell, Dr. Sabeti said, especially without data on the effectiveness of the approach. So she and her colleagues decided to gather some.

“Fundamentally, the paper is about the intersection of kindness and success — how being generous with one’s resources actually is the most effective” strategy, said Kian Sani, one of the study’s authors.
“Fundamentally, the paper is about the intersection of kindness and success — how being generous with one’s resources actually is the most effective” strategy, said Kian Sani, one of the study’s authors.Pete Kiehart for The New York Times

They developed an epidemiological model to simulate how a virus might spread through a midsize university, like Colorado Mesa University, one of the schools Dr. Sabeti’s team has been advising. (Several C.M.U. officials and researchers are co-authors of the paper.)

Using real-world data from C.M.U., the researchers created a baseline scenario in which 1 percent of people at the school, and 6 percent of those in the surrounding county, were infected by the coronavirus, and the university was testing 12 percent of its members every day. The team assumed that they had a complete list of each university member’s close off-campus contacts, and that if someone tested positive for the virus, they and their contacts would quarantine until they were no longer infectious.

Under these conditions, the researchers found, if the university used all of its tests on its own members, it would have roughly 200 Covid-19 cases after 40 days. But if instead it parceled out some of those tests, using them on community members who were close contacts of students and staff, the number of cases dropped by one-quarter.

“The optimal proportion of tests to use outside the institution on those targeted, first-degree contacts came out to be about 45 percent,” said Ivan Specht, an undergraduate researcher in Dr. Sabeti’s lab and a co-author of the paper. In short, institutions could reduce their caseloads by one-fourth if they used almost half their tests on people just outside their direct membership. That percentage “is remarkably high considering that most institutions use zero percent of their tests outside of themselves,” Mr. Specht noted.

The researchers then tweaked the model’s parameters in various ways: What if the virus were more prevalent? What if students and staff did not report all their contacts? What if they were better about mask-wearing and social distancing? What if the university deployed more tests, or fewer?

Unsurprisingly, the more testing the university did, and the more information it had about its members’ close contacts, the fewer Covid-19 cases there were. But in virtually every scenario, sharing at least some tests with the broader community led to fewer cases than hoarding them.

“The surprising thing is just how robust that finding is in the face of some pretty plausible variations,” said A. David Paltiel, a professor of health policy and management at Yale School of Public Health, who was not involved in the study.

Still, he noted, there were plenty of scenarios that the model didn’t test, and the paper still needs to undergo a thorough peer review.

Its predictions should also be tested in the real world, Dr. O’Connor said: “It needs to be explored and tested head-to-head with other allocation methods.”

But if the findings hold up, it would suggest that schools and other institutions that are trying to reopen safely should think beyond their own walls when they develop testing programs. “Even if your goal is only to protect the students in your care, you will still be doing the maximum to protect those students by taking care of the people in the surrounding community,” Dr. Paltiel said. “That’s a pretty strong argument.”

Some universities are beginning to adopt this outlook. C.M.U. now offers free tests to all of its students’ self-reported contacts, whether or not they are affiliated with the university, and runs a testing site that is open to local residents, said Amy Bronson, a co-chair of the university’s Covid-19 task force and an author of the paper.

And in November, the University of California, Davis, began offering free coronavirus tests to anyone who lives or works in the city. The Healthy Davis Together program, a partnership with the city, has since administered more than 450,000 tests and identified more than 1,000 people with the virus, said Brad Pollock, an epidemiologist at U.C. Davis who directs the project.

“A virus does not respect geographic boundaries,” Dr. Pollock said. “It is ludicrous to think that you can get control of an acute infectious respiratory disease like Covid-19, in a city like Davis that hosts a very large university, without coordinated public health measures that connect both the university and the community.”

There are barriers to the more altruistic approach, including internal political pressure to use testing resources in house and concerns about legal liability. But the researchers hope that their model convinces at least some institutions to rethink their strategy, not only during this epidemic but also in future ones.

“An outbreak is an opportunity to buy a lot of community good will, or to burn a lot of community good will,” Dr. Sabeti said. “We could have spent an entire year building up that relationship between organizations and institutions and their communities. And we would have done all that hard work together, as opposed to everybody turning inward.”

Virus Variants Likely Evolved Inside People With Weak Immune Systems

Virus Variants Likely Evolved Inside People With Weak Immune Systems

Growing evidence suggests that people with cancer and other conditions that challenge their immune systems may be incubators of mutant viruses.

A Covid patient in the I.C.U. of Sarasota Memorial Hospital in Florida last month.
A Covid patient in the I.C.U. of Sarasota Memorial Hospital in Florida last month.Credit…Shannon Stapleton/Reuters
Apoorva Mandavilli

  • March 15, 2021, 3:23 p.m. ET

The version of the coronavirus that surfaced in Britain late last year was shocking for many reasons. It came just as vaccines had offered a glimpse of the end of the pandemic, threatening to dash those hopes. It was far more contagious than earlier variants, leading to a swift increase in hospitalizations. And perhaps most surprising to scientists: It had amassed a large constellation of mutations seemingly overnight.

A coronavirus typically gains mutations on a slow-but-steady pace of about two per month. But this variant, called B.1.1.7, had acquired 23 mutations that were not on the virus first identified in China. And 17 of those had developed all at once, sometime after it diverged from its most recent ancestor.

Experts said there’s only one good hypothesis for how this happened: At some point the virus must have infected someone with a weak immune system, allowing it to adapt and evolve for months inside the person’s body before being transmitted to others. “It appears to be the most likely explanation,” said Dr. Ravindra Gupta, a virologist at the University of Cambridge.

If true, the idea has implications for vaccination programs, particularly in countries that have not yet begun to immunize their populations. People with compromised immune systems — such as cancer patients — should be among the first to be vaccinated, said Dr. Adam Lauring, a virologist and infectious disease physician at the University of Michigan. The faster that group is protected, the lower the risk that their bodies turn into incubators for the world’s next supercharged mutant.

“We should give the best shot we can, both literally and figuratively, to protect this population,” Dr. Lauring said.

That might be complicated, he added. For the same reason that these people don’t mount a strong immune response to the virus, vaccines might not work well in them. So they may need to be treated with cocktails of monoclonal antibodies as well, he said.

Like other viruses, the coronavirus collects mutations every time it replicates. The overwhelming majority of those genetic glitches are insignificant and transient. In most people, an active infection lasts only about a week, not long enough for the virus to acquire more than one noteworthy mutation, if any.

Mutations that make the coronavirus more contagious or enable it to dodge the immune system are extremely rare, researchers reported in a study published last week in the journal Science. “But if they do occur, and if they can get transmitted, then it’s open season,” said Katrina Lythgoe, an evolutionary biologist at the University of Oxford who led the study.

Over a period of months to years, the virus may string together several such mutations. Scientists can observe this slow evolution using a molecular “clock” that captures the changes over time. But in a person with a weak immune system, this timeline can be greatly accelerated.

Multiple studies have shown that in some people who are immunocompromised, the virus can persist for more than eight months, ample time and opportunity to keep evolving.

“If we look at several time points through that course of infection, and we look at the virus population in that patient, we see — every time — different variants popping up with a large turnover rate,” said Vincent Munster, a virologist at the National Institute of Allergy and Infectious Diseases who led one of the studies.

If one of these variants that has gained important mutations is transmitted to someone else, it may spread quickly through the population and seem to have emerged out of nowhere — as in the case of the variant that walloped Britain, and perhaps others identified in South Africa and Brazil.

“That’s a pretty decent hypothesis that they’ve come from people with persistent infection,” Dr. Lythgoe said of the variants. “By keeping infection rates low, you’re going to reduce the number of immunocompromised people who are infected and reduce the chance that they occur.”

“Immunocompromised” is a nebulous term encompassing a wide range of conditions — from diabetes and rheumatoid arthritis to leukemia and lymphoma — and experts disagreed on which conditions may lead to variants.

Some say the list should include older people, as well as those who take medications that suppress the immune system and anyone who does not produce a robust set of antibodies.

“We learned from the vaccines that antibodies matter,” said Paul Duprex, director of the Center for Vaccine Research at the University of Pittsburgh. “It’s very important to keep an eye on people who are immune-suppressed, who don’t have fully functional immune systems.”

Dr. Lauring said he was most worried about people with blood-related cancers like leukemia, but did not have strong concerns about those taking drugs like Humira or Enbrel, which are used to treat rheumatoid arthritis.

“It’s a different kind of immunosuppression that I’m not sure would lead to this, but no one knows for sure,” he said.

Some people with weak immune systems have been known to transmit other viruses over long periods, Dr. Lauring noted. One man in England has shed poliovirus for at least 28 years. Others have had persistent infections with norovirus or influenza.

“We’ve been dealing with this for a long time,” he said. “But just like everything with Covid, we’re dealing with it on a big scale.”

He and the other experts emphasized that regardless of the risks, it is important not to stigmatize or blame people who have compromised immune systems. Instead, they said, the focus should be on limiting their exposure to the virus.

“Let’s get the vaccines into people, let’s do good distancing, let’s do good masking,” Dr. Duprex said. “Everything that we can do to stop the virus spreading is really very important.”

Plan to Ditch the Mask After Vaccination? Not So Fast.

Plan to Ditch the Mask After Vaccination? Not So Fast.

It’s not clear how easily vaccinated people may spread the virus, but the answer to that question is coming soon. Until then, scientists urge caution.

A health care worker prepared a dose of the Pfizer-BioNTech vaccine at a vaccination site in San Francisco on Monday.
A health care worker prepared a dose of the Pfizer-BioNTech vaccine at a vaccination site in San Francisco on Monday.Credit…Mike Kai Chen for The New York Times
Apoorva Mandavilli

  • March 3, 2021, 3:23 p.m. ET

With 50 million Americans immunized against the coronavirus, and millions more joining the ranks every day, the urgent question on many minds is: When can I throw away my mask?

It’s a deeper question than it seems — about a return to normalcy, about how soon vaccinated Americans can hug loved ones, get together with friends, and go to concerts, shopping malls and restaurants without feeling threatened by the coronavirus.

Certainly many state officials are ready. On Tuesday, Texas lifted its mask mandate, along with all restrictions on businesses, and Mississippi quickly followed suit. Governors in both states cited declining infection rates and rising numbers of citizens getting vaccinated.

But the pandemic is not yet over, and scientists are counseling patience.

It seems clear that small groups of vaccinated people can get together without much worry about infecting one another. The Centers for Disease Control and Prevention is expected shortly to issue new guidelines that will touch on small gatherings of vaccinated Americans.

But when vaccinated people can ditch the masks in public spaces will depend on how quickly the rates of disease drop and what percentage of people remain unvaccinated in the surrounding community.

Why? Scientists do not know whether vaccinated people spread the virus to those who are unvaccinated. While all of the Covid-19 vaccines are spectacularly good at shielding people from severe illness and death, the research is unclear on exactly how well they stop the virus from taking root in an immunized person’s nose and then spreading to others.

It’s not uncommon for a vaccine to forestall severe disease but not infection. Inoculations against the flu, rotavirus, polio and pertussis are all imperfect in this way.

The coronavirus vaccines “are under a lot more scrutiny than any of the previous vaccines ever have been,” said Neeltje van Doremalen, an expert in preclinical vaccine development at the National Institutes of Health’s Rocky Mountain Laboratories in Montana.

And now coronavirus variants that dodge the immune system are changing the calculus. Some vaccines are less effective at preventing infections with certain variants, and in theory could allow more virus to spread.

The research available so far on how well the vaccines prevent transmission is preliminary but promising. “We feel confident that there’s a reduction,” said Natalie Dean, a biostatistician at the University of Florida. “We don’t know the exact magnitude, but it’s not 100 percent.”

Still, even an 80 percent drop in transmissibility might be enough for immunized people to toss their masks, experts said — especially once a majority of the population is inoculated, and as rates of cases, hospitalizations and deaths plummet.

A line to register for a vaccination appointment in San Francisco. Experts say that people who have been inoculated should continue to wear masks to protect others.
A line to register for a vaccination appointment in San Francisco. Experts say that people who have been inoculated should continue to wear masks to protect others.Credit…Mike Kai Chen for The New York Times

But most Americans are still unvaccinated, and more than 1,500 people are dying every day. So given the uncertainty around transmission, even people who are immunized must continue to protect others by wearing masks, experts said.

“They should wear masks until we actually prove that vaccines prevent transmission,” said Dr. Anthony S. Fauci, director of the National Institute for Allergy and Infectious Diseases.

That proof is not yet in hand because the clinical trials for vaccines were designed to test whether the vaccines prevent serious illness and death, which usually reflects the virus’s impact on the lungs. Transmission, on the other hand, is driven by its growth in the nose and throat.

Primed by the vaccine, the body’s immune fighters should curb the virus soon after infection, shortening the infection period and curtailing the amounts in the nose and throat. That ought to significantly reduce the chances that a vaccinated person might infect others.

Animal studies support the theory. In one study, when monkeys were immunized and then exposed to the virus, seven of eight animals had no detectable virus in their noses or lung fluid, noted Juliet Morrison, a virologist at the University of California, Riverside.

Similarly, data from a few dozen participants in the Moderna trial who were tested when they got their second doses suggested that the first dose had decreased cases of infection by about two-thirds.

Another small batch of data emerged recently from the Johnson & Johnson trial. Researchers looked for signs of infection in 3,000 participants up to 71 days after getting the single-dose vaccine. Risk of infection in that study seemed to fall by about 74 percent.

“I think that’s very powerful,” said Dan Barouch, a virologist at Beth Israel Medical Center in Boston, who led one of the trial sites. “Those number estimates could change with more data, but the effect seems quite strong.”

More data is expected in the coming months from both Pfizer-BioNTech and Moderna.

But clinical trials may overestimate the power of a vaccine, because the type of people who choose to participate already tend to be careful and are counseled on precautions during the trial.

Some researchers instead are tracking infections among immunized people in real-world settings. For example, a study in Scotland conducted tests every two weeks, regardless of symptoms, on health care workers who had received the Pfizer-BioNTech vaccine. Investigators found that the vaccine’s effectiveness in preventing infection was 70 percent after one dose, and 85 percent after the second.

Researchers in Israel assessed infections in almost 600,000 immunized people and tried to trace their household contacts. The scientists found a 46 percent drop in infections after the first dose and a 92 percent drop after the second. (The study may have missed infections in people without symptoms.)

But to get a true assessment of transmission, researchers really need to know which immunized people become infected, and then trace the spread of the virus among their contacts with genetic analysis.

“That’s the ideal way to actually do this,” said Dr. Larry Corey, an expert in vaccine development at The Fred Hutchinson Cancer Research Center in Seattle. He is hoping to conduct such a study in college-age students.

Preparing swab samples at a testing site in San Francisco on Tuesday.Credit…Mike Kai Chen for The New York Times

But what precautions should immunized people take until the results from such studies become available? At the moment, many experts believe that what’s permissible will depend to a large extent on the number of cases in the surrounding community.

The higher the number of cases, the greater the likelihood of transmission — and the more effective vaccines must be in order to stop the spread.

“If the case numbers are zero, it doesn’t matter whether it’s 70 percent or 100 percent,” said Zoe McLaren, a health policy expert at the University of Maryland, referring to vaccine effectiveness.

Mask-wearing policies also will depend on how many unvaccinated people remain in the population. Americans may need to remain cautious as long as vaccination rates are low. But people will be able to relax a bit as those rates rise, and begin to return to normalcy once the virus runs out of others to infect.

“A lot of people have in mind that masks are the first thing that you let up on,” Dr. MacLaren said. In fact, she said, masks provide more freedom by allowing people to go to concerts, travel on buses or airplanes, or go shopping even with unvaccinated people around.

Ultimately, masks are a form of civic responsibility, said Sabra Klein, an immunologist at the Johns Hopkins Bloomberg School of Public Health.

“Are you wearing a mask to protect yourself from severe Covid, or are you wearing a mask for public health?” Dr. Klein said. “It’s right to do your part in the community beyond yourself.”

Scientists to C.D.C.: Set Air Standards for Workplaces Now

Scientists to C.D.C.: Set Air Standards for Workplaces Now

The agency has not fully reckoned with airborne transmission of the coronavirus in settings like hospitals, schools and meatpacking plants, experts said.

Production of N95 masks at a facility in Fort Worth, Texas, earlier this month. “It’s time to stop pussyfooting around the fact that the virus is transmitted mostly through the air,” said one expert.
Production of N95 masks at a facility in Fort Worth, Texas, earlier this month. “It’s time to stop pussyfooting around the fact that the virus is transmitted mostly through the air,” said one expert.Credit…Cooper Neill for The New York Times
Apoorva Mandavilli

  • Feb. 17, 2021, 12:01 a.m. ET

Nearly a year after scientists showed that the coronavirus can be inhaled in tiny droplets called aerosols that linger indoors in stagnant air, more than a dozen experts are calling on the Biden administration to take immediate action to limit airborne transmission of the virus in high-risk settings like meatpacking plants and prisons.

The 13 experts — including several who advised President Biden during the transition — urged the administration to mandate a combination of masks and environmental measures, like better ventilation, to blunt the risks in various workplaces.

On Friday, the Centers for Disease Control and Prevention issued new guidelines for reopening schools, but quickly passed over improved ventilation as a precaution. It was only in July that the World Health Organization conceded that the virus can linger in the air in crowded indoor spaces, after 239 experts publicly called on the organization to do so.

In a letter to the administration, scientists detailed evidence supporting airborne transmission of the virus. It has become even more urgent for the administration to take action now, the experts said, because of the slow vaccine rollout, the threat of more contagious variants of the virus already circulating in the United States, and the high rate of Covid-19 infections and deaths, despite a recent drop in cases.

“It’s time to stop pussyfooting around the fact that the virus is transmitted mostly through the air,” said Linsey Marr, an expert on aerosols at Virginia Tech.

“If we properly acknowledge this, and get the right recommendations and guidance into place, this is our chance to end the pandemic in the next six months,” she added. “If we don’t do this, it could very well drag on.”

The letter was delivered on Monday to Jeffrey D. Zients, coordinator of the Biden administration’s Covid-19 response; Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention; and Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases.

Dr. Anthony S. Fauci, left, and Jeffrey D. Zients, President Biden’s Covid-19 response coordinator, at the White House last month.
Dr. Anthony S. Fauci, left, and Jeffrey D. Zients, President Biden’s Covid-19 response coordinator, at the White House last month.Credit…Doug Mills/The New York Times

The letter urged the C.D.C. to recommend the use of high-quality masks, such as N95 respirators, to protect workers at high risk of infection. At present, health care workers mostly rely on surgical masks, which are not as effective against aerosol transmission of the virus.

Many workers vulnerable to infection are people of color, who have borne the brunt of the epidemic in the United States, the experts noted.

Mr. Biden has directed the Occupational Safety and Health Administration, which sets workplace requirements, to issue emergency temporary standards for Covid-19, including those regarding ventilation and masks, by March 15.

But OSHA will only mandate standards that are supported by guidance from the C.D.C., said David Michaels, an epidemiologist at George Washington University and one of the signatories.

(Dr. Michaels led OSHA during the Obama administration; the agency has not had a permanent leader since his departure.)

“Until the C.D.C. makes some changes, OSHA will have difficulty changing the recommendations it puts up because there’s an understanding the government has to be consistent,” Dr. Michaels said. “And C.D.C. has always been seen as the lead agency for infectious disease.”

Public health agencies, including the W.H.O., have been slow to acknowledge the importance of aerosols in spreading the coronavirus. It was only in October that the C.D.C. recognized that the virus can sometimes be airborne, after a puzzling sequence of events in which a description of how the virus spreads appeared on the agency’s website, then vanished, then resurfaced two weeks later.

But the agency’s recommendations on workplace accommodations did not reflect this change.

Early in the pandemic, the C.D.C. said health care workers did not need N95 respirators, and could even wear bandannas to protect themselves. It also did not recommend face coverings for the rest of the population.

The agency has since revised those recommendations. It recently recommended that people wear two masks or improve the fit of their surgical masks to protect from the virus.

“But they don’t talk about why you need a better fitting mask,” said Dr. Donald Milton, an aerosol expert at the University of Maryland. “They’re acknowledging the importance of breathing it in and the route of transmission, and yet they don’t say it clearly in their various web pages.”

Election workers in Lansing, Mich., sorted absentee ballots in November while a ventilation duct helped to circulate air.Credit…John Moore/Getty Images

The agency recommends surgical masks for health care workers and says N95 respirators are needed only during medical procedures that generate aerosols, like certain kinds of surgery.

But many studies have shown that health care workers who have no direct contact with Covid-19 patients are also at high risk of infection and should be wearing high-quality respirators, said Dr. Céline Gounder, an infectious disease specialist at Bellevue Hospital Center in New York and an adviser to Mr. Biden during the transition.

“The C.D.C. has not emphasized the risk of aerosol transmission enough,” Dr. Gounder said. “Unfortunately, concerns about supply continue to muddy the discussion.”

Many hospitals still expect their staff to reuse N95 masks per the agency’s recommendation to reuse when supplies are low. But since the masks are no longer in short supply, the agency should change its recommendations, Dr. Gounder said.

“We really do need to stop this reuse and decontamination approach to N95s,” she added. “We’re a year into this, and that’s really not acceptable.”

Hospitals, at least, tend to have good ventilation so health care workers are protected in other ways, the experts said. But in meatpacking plants, prisons, buses or grocery stores, where workers are exposed to the virus for long periods of time, the C.D.C. does not recommend high-quality respirators, nor does it endorse upgrades to ventilation.

“If you go to other workplaces, this idea that aerosol transmission is important is virtually unknown,” Dr. Michaels said. In food processing plants, for example, a refrigerated environment and the lack of fresh air are ideal conditions for the virus to thrive. But the industry has not put in safety measures to minimize the risk, he added.

Employers instead hew to the C.D.C.’s recommendations for physical distancing and cleaning surfaces.

The recent emergence of more contagious variants makes it urgent for the C.D.C. to address airborne transmission of the virus, said Dr. Marr of Virginia Tech. Germany, Austria and France now mandate N95 respirators or other high-quality masks in public transportation and shops.

Dr. Marr was one of the experts who wrote to the W.H.O. last summer to push for an acknowledgment of airborne transmission. She did not expect to be in a similar position again so many months later, she said: “It feels like Groundhog Day.”

Covid-Linked Syndrome in Children Is Growing and Cases Are More Severe

Covid-Linked Syndrome in Children Is Growing and Cases Are More Severe

The condition, which usually emerges several weeks after infection, is still rare, but can be dangerous. “A higher percentage of them are really critically ill,” one doctor said.

Braden Wilson, of Simi Valley, Calif., with his mother, Amanda. He was hospitalized and placed on a ventilator and a heart-lung bypass machine, but he died on Jan. 5. “My boy was gone,” his mother recalled.
Braden Wilson, of Simi Valley, Calif., with his mother, Amanda. He was hospitalized and placed on a ventilator and a heart-lung bypass machine, but he died on Jan. 5. “My boy was gone,” his mother recalled.Credit…via Amanda Wilson
Pam Belluck

  • Feb. 16, 2021, 3:00 a.m. ET

Fifteen-year-old Braden Wilson was frightened of Covid-19. He was careful to wear masks and only left his house, in Simi Valley, Calif., for things like orthodontist checkups and visits with his grandparents nearby.

But somehow, the virus found Braden. It wreaked ruthless damage in the form of an inflammatory syndrome that, for unknown reasons, strikes some young people, usually several weeks after infection by the coronavirus.

Doctors at Children’s Hospital Los Angeles put the teenager on a ventilator and a heart-lung bypass machine. But they could not stop his major organs from failing. On Jan. 5, “they officially said he was brain dead,” his mother, Amanda Wilson, recounted, sobbing. “My boy was gone.”

Doctors across the country have been seeing a striking increase in the number of young people with the condition Braden had, which is called Multisystem Inflammatory Syndrome in Children or MIS-C. Even more worrisome, they say, is that more patients are now very sick than during the first wave of cases, which alarmed doctors and parents around the world last spring.

“We’re now getting more of these MIS-C kids, but this time, it just seems that a higher percentage of them are really critically ill,” said Dr. Roberta DeBiasi, chief of infectious diseases at Children’s National Hospital in Washington, D.C. During the hospital’s first wave, about half the patients needed treatment in the intensive care unit, she said, but now 80 to 90 percent do.

The reasons are unclear. The surge follows the overall spike of Covid cases in the United States after the winter holiday season, and more cases may simply increase chances for severe disease to emerge. So far, there’s no evidence that recent coronavirus variants are responsible, and experts say it is too early to speculate about any impact of variants on the syndrome.

The condition remains rare. The latest numbers from the Centers for Disease Control and Prevention show 2,060 cases in 48 states, Puerto Rico and the District of Columbia, including 30 deaths. The median age was 9, but infants to 20-year-olds have been afflicted. The data, which is complete only through mid-December, shows the rate of cases has been increasing since mid-October.

While most young people, even those who became seriously ill, have survived and gone home in relatively healthy condition, doctors are uncertain whether any will experience lingering heart issues or other problems.

“We really don’t know what will happen in the long term,” said Dr. Jean Ballweg, medical director of pediatric heart transplant and advanced heart failure at Children’s Hospital & Medical Center in Omaha, Neb., where from April through October, the hospital treated about two cases a month, about 30 percent of them in the I.C.U. That rose to 10 cases in December and 12 in January, with 60 percent needing I.C.U. care — most requiring ventilators. “Clearly, they seem to be more sick,” she said.

Symptoms of the syndrome can include fever, rash, red eyes or gastrointestinal problems. Those can progress to heart dysfunction, including cardiogenic shock, in which the heart cannot squeeze enough to pump blood sufficiently. Some patients develop cardiomyopathy, which stiffens the heart muscle, or abnormal rhythm. Dr. Ballweg said one 15-year-old at her hospital needed a procedure that functioned as a temporary pacemaker.

Jude Knott, 4, at home with his mother, Ashley Knott, was hospitalized for 10 days after developing a headache, fever, vomiting, red eyes and a rapid heart rate.
Jude Knott, 4, at home with his mother, Ashley Knott, was hospitalized for 10 days after developing a headache, fever, vomiting, red eyes and a rapid heart rate.Credit…Kathryn Gamble for The New York Times

Hospitals say most patients test positive for Covid antibodies that indicate previous infection, but some patients also test positive for active coronavirus infection. Many children were previously healthy and had few or no symptoms from their initial Covid infection. Doctors are uncertain which factors predispose children to the syndrome. Dr. Jane Newburger, associate chief for academic affairs in Boston Children’s Hospital’s cardiology department, who is a leader of a nationwide study, said patients with obesity and some older children seem to fare worse.

Sixty-nine percent of reported cases have affected Latino or Black young people, which experts believe stems from socioeconomic and other factors that have disproportionately exposed those communities to the virus. But Omaha’s hospital, where early cases were largely among children of Latino parents working in the meatpacking industry, is now “seeing a much more broad spectrum and every ethnicity,” Dr. Ballweg said.

Jude Knott, 4, was hospitalized in Omaha for 10 days after developing a headache, fever, vomiting, red eyes and a rapid heart rate.

“It was just a roller coaster,” said his mother, Ashley Knott, a career coach at an Omaha nonprofit helping low-income teenagers.

To explain to Jude the infusions of intravenous immunoglobulin doctors were giving him, she said they were “‘putting Ninjas in your blood so they can fight.’” For blood thinner injections, which he hated, she said, “‘Buddy, they’re making your blood go from a milkshake to water because we need it to be water.’ Anything to help him make sense of it.”

Jude recently returned to preschool full time. He has some dilation of a coronary artery, but is improving, his mother said.

“He’s definitely experiencing some anxiety,” Ms. Knott said. “I just worry that he’s kind of been saddled with some adult worries at 4.”

Doctors said they’ve learned effective treatment approaches, which, besides steroids, immunoglobulin and blood thinners, can include blood pressure medications, an immunomodulator called anakinra and supplemental oxygen. Some hospitals use ventilators more than others, experts said.

But though doctors are learning more, pediatricians can miss the syndrome initially because early symptoms can mimic some common ailments.

Mayson Barillas, 11, was hospitalized for eight days at Children’s National Hospital, where his doctors said he exhibited cardiogenic shock.Credit…Rosem Morton for The New York Times

On New Year’s Day, Mayson Barillas, 11, of Damascus, Md., started feeling sick. “My stomach started hurting, and then I went to my soccer game and then I got a fever,” he said.

His mother, Sandy Barillas, a medical assistant at a women’s health practice, gave him Alka Seltzer, Pepto Bismol and Tylenol. Several days later, he developed shortness of breath and they went to an urgent care clinic.

There, a rapid Covid-19 test was negative, as were evaluations for strep, influenza and appendicitis. Ms. Barillas said she was told, “It was just like a stomach flu.”

But the next day, Mayson had swollen eyes and lips with red blisters. “He started developing really bad body aches and he couldn’t walk anymore,” she said. She took him to an emergency room, which transferred him to Children’s National Hospital, where doctors said he exhibited cardiogenic shock.

“It was very scary,” Ms. Barillas said. “I’d never heard of this syndrome before.”

Mayson spent eight days in the hospital, four in the I.C.U. Since leaving, he has seen a hematologist, a rheumatologist and a cardiologist and is on blood thinners for now. The hardest part, said Mayson, a star local soccer player, is being temporarily sidelined from sports, as doctors advise for most patients for several months.

“It was very shocking for everybody in the community: ‘Wow, how did this happen to someone very healthy?’” Ms. Barillas said.

At a memorial service on Feb. 5, Braden Wilson was remembered as a kindhearted, creative teenager who loved filmmaking and fashion. His color-splashed oil paintings were displayed.

His mother read a poem he wrote that hangs on the refrigerator of his grandparents, Fabian and Joe Wilson, with whom he was close: “Hold fast to dreams/ for if dreams create/ life is a beautiful canvas/ a masterpiece painted great.”

Braden at his eighth-grade graduation with his grandparents, Fabian and Joe Wilson, with whom he was close.Credit…via Amanda Wilson

It’s unclear why the syndrome hit Braden so hard. Ms. Wilson said he did not have serious health issues. She said he was overweight but active, swimming three times a week and taking dance and yoga at his arts-and-science high school.

Symptoms started New Year’s Eve, when he began vomiting and spiking a fever. Ms. Wilson took him to an emergency room, where he tested positive for the coronavirus, received treatment that included a new monoclonal antibody drug and was sent home.

But his fever persisted and two days later, he developed diarrhea and his lips and fingers turned blue. Ms. Wilson called 911. When paramedics arrived, she said, he was “lying in his bed, like almost lifeless.”

At the hospital, he was hooked to a ventilator and transferred to Children’s Hospital Los Angeles, which like several hospitals has established a MIS-C clinic with various specialists.

“Braden was one of our most ill patients,” said Dr. Jacqueline Szmuszkovicz, a pediatric cardiologist there.

Doctors placed him on the heart-lung bypass machine, put him on dialysis and performed a heart procedure to relieve pressure. “He had what we would term severe multisystem organ failure: his lungs, his heart, his kidneys,” Dr. Szmuszkovicz said.

Through tears, Ms. Wilson said that after a few days, Braden began bleeding from his mouth, eyes and nose, and doctors ultimately could not detect brain activity. “I asked them specifically: ‘Is there any chance for him to recover from this?’” she recounted. “And they said no.”

Family members FaceTimed to say goodbye before life support was withdrawn. Ms. Wilson gave consent for doctors to take blood samples from his body for research studies.

Ms. Wilson had never written poetry before, but since Braden’s death, it has spilled out of her.

“Now your heart no longer beats / and I can’t hold you in my arms,” reads one. “But I remember back to those days / When my womb protected you from harm/ You lived a life of beauty/ of laughter, and of grace/ I hold you now inside my heart / We’ll always share that space.”

C.D.C. Draws Up a Blueprint for Reopening Schools

C.D.C. Draws Up a Blueprint for Reopening Schools

Amid an acrid national controversy, the agency proposed detailed criteria for returning students to classrooms.

Students returning to P.S. 189 in Brooklyn in December, when New York City reopened its schools after rising infection rates had forced a closure.
Students returning to P.S. 189 in Brooklyn in December, when New York City reopened its schools after rising infection rates had forced a closure.Credit…Victor J. Blue for The New York Times
  • Feb. 12, 2021, 2:14 p.m. ET

The Centers for Disease Control and Prevention on Friday urged that K-12 schools be reopened and offered a comprehensive science-based plan for doing so speedily, an effort to resolve an urgent debate roiling in communities across the nation.

The new guidelines highlight the growing body of evidence that schools can openly safely if they put in effect layered mitigation measures. The agency said that even when students lived in communities with high transmission rates, elementary students could receive at least some in-person instruction safely.

And middle and high school students, the agency said, could attend school safely at most lower levels of community transmission — or even at higher levels, if schools put into effect weekly testing of staff and students to identify asymptomatic infections.

“CDC’s operational strategy is grounded in science and the best available evidence,” Dr. Rochelle Walensky, director of the C.D.C., said on Friday in a call with reporters.

The guidelines arrive in the middle of a debate that is already highly fraught. Some parents whose schools remain closed are becoming increasingly frustrated, and public school enrollment has declined in many districts across the country. Education and civil rights leaders are despairing about the harms being done to children who have not been in classrooms for nearly a year.

And teachers’ unions in some places are fighting against reopening schools before teachers can be fully vaccinated.

The Biden administration has made a high priority of returning children to classrooms, and the new recommendations try to carve a middle ground between school officials as well as some parents who are eager to see a resumption of in-person learning and powerful teachers’ unions resisting a return to school settings that they regard as unsafe amid the coronavirus pandemic.

Whether the guidelines will persuade powerful teachers’ unions — allies of Mr. Biden — to support teachers returning to classrooms remains to be seen. In advice that may be disappointing to some unions, the document states that, while teachers should be vaccinated as quickly as possible, teachers do not need to be vaccinated before schools can reopen.

The document embraces the often-repeated mantra that schools should be the last settings to close in a community and the first to reopen. But that has been followed nowhere in the country, and these guidelines have no power to force communities where transmission remains high to take steps, such as closing nonessential businesses, to decrease it.

As a result, some teachers’ unions will continue to argue that the overall environment remains unsafe to return to in-person classrooms.

A majority of districts in the country are offering at least some in-person learning, and about half of the nation’s students are learning in classrooms. But there are stark disparities in who has access to in-person instruction, with urban districts, which serve mostly poor, nonwhite children, more likely to be closed than nonurban ones.

Those are some of the places where education experts are most concerned about the consequences of students being out of school for such a prolonged period. There is growing evidence that some students who are learning remotely are falling significantly behind academically.

And, while data are still very limited, many doctors and mental health experts report seeing unusually high numbers of children and adolescents who are depressed, anxious or experiencing other mental health issues.

At the same time, many parents in urban districts, particularly poor and nonwhite parents, remain hesitant to send their children back to school even if given the option, out of fear that their children can get sick and possibly bring home the virus.

Schools have reopened partially or are starting to reopen in New York City, Chicago, Boston and other cities. But conflict between elected officials who support reopening and teachers’ unions seems likely to continue in places like Los Angeles, San Francisco and Portland, despite the new guidelines.

School district leaders have long asked for clearer guidelines from the federal government on how they should make decisions during the pandemic. The C.D.C.’s advice comes as a relief to many experts who have been frustrated at the low priority given to schools in local reopening plans.

“It’s not saying if you open schools again,” said Helen Jenkins, an infectious disease expert at Boston University and an adviser to the public schools district in Cambridge, Mass. “It’s saying, ‘You are going to open schools again, and this is how to do it,’ which I appreciate.”

The agency’s approach struck the right balance between the risks and the benefits of in-person instruction, said Jennifer Nuzzo, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health.

“We have accumulated a tremendous amount of harms from not having schools open,” Dr. Nuzzo said. “This document is important in trying to couch the risks in relation to those harms, and try to paint a path forward.”

The C.D.C. encouraged elementary schools to remain open regardless of virus levels in the surrounding community, pointing to evidence that young students are least likely to be infected or to spread the virus. Middle schools and high schools should switch to virtual learning only when community transmission of the coronavirus reaches the highest level, the agency said.

The agency also prioritized in-person instruction over extracurricular activities like sports and school events. In an outbreak, these activities should be curtailed before classrooms are closed, officials said.

Some experts raised concerns about the strategy.

Most school districts are in communities where viral transmission is already at or close to levels that the agency has deemed to be the highest risk, for example. Yet many have kept schools open without experiencing outbreaks of the virus.

“Most of the United States is sending their kids to school at above that cutoff,” said Dr. Jacqueline Grupp-Phelan, chief of pediatric emergency medicine at the University of California, San Francisco. “I’m not sure it’s going to make an impact on them, because they’re doing it and they’ve done it safely.”

Teachers and supporters demonstrating this month outside Samuel Gompers Public School in Philadelphia. Notably absent from the C.D.C. guidance are recommendations on improving ventilation in schools.
Teachers and supporters demonstrating this month outside Samuel Gompers Public School in Philadelphia. Notably absent from the C.D.C. guidance are recommendations on improving ventilation in schools.Credit…Matt Rourke/Associated Press
Cecilia Krizmanich, left, a teacher at Joyce Kilmer Elementary in Chicago, helped set up Marvin Araujo-Avilas’s computer on the first day of in-person classes on Thursday. Only two students showed up. Credit…Taylor Glascock for The New York Times

Notably absent from the agency’s guidance were recommendations on improving ventilation in schools, an important safeguard now that the coronavirus is known to be carried aloft in tiny airborne particles.

In one short paragraph, the C.D.C. suggested that schools open windows and doors to increase circulation, but said they should not be opened “if doing so poses a safety risk or a health risk.”

“C.D.C. gives lip service to ventilation in its report, and you have to search to find it,” said Joseph Allen, an expert on building safety at the Harvard T.H. Chan School of Public Health in Boston. “It’s not as prominent as it should be.”

The section on ventilation does link to more information online. But all of that is buried, relative to a misguided emphasis on cleaning surfaces like outdoor playground equipment, said Linsey Marr, an expert in airborne transmission of viruses at Virginia Tech.

“I think the balance is incorrect in putting so much emphasis on cleaning surfaces and almost no emphasis on cleaning the air, given what we know about how the virus spreads,” she said.

Ideally, the C.D.C. should also have mentioned high-quality masks or double-masking, Dr. Allen said. (The agency on Thursday released new advice for masking that included the use of two masks at once.)

Other preventive measures the C.D.C. recommended for schools are those it has previously endorsed: universal masking of staff and students; physical distancing; hand-washing and hygiene; cleaning; and contact tracing, in combination with isolation for those who have tested positive and quarantine for those who have been exposed to the virus.

The agency advised that schools refer all symptomatic students, teachers, staff and close contacts for diagnostic testing, and that schools put in place routine weekly testing of students and staff, except when community transmission is low. But the expense and logistics of widespread screening would be a heavy burden for school districts.

The C.D.C. skated lightly over physical distancing. “The agency’s previous recommendation for distancing suggested that schools have students attend on alternating schedules, in order to reduce the number of students in classrooms and hallways.”

The new guidance instead says schools should put in effect physical distancing “to the greatest extent possible,” but requires it only when community transmission of the virus is high. The softer emphasis makes the guidelines more feasible for school districts to follow, Dr. Nuzzo said.

“A lot of communities have pursued hybrid approaches, or in some cases just not opened, because they haven’t been able to figure out that spacing issue,” she said. The guidelines give the impression that maintaining at least six feet of distance between students is ideal, “but the whole attempt to bring kids back to school doesn’t have to break down over that,” she added.

The six-feet rule has been embraced as an orthodoxy, however, by many educators. Becky Pringle, president of the National Education Association, the country’s largest teachers union, said there should be no wiggle room on physical distancing or other mitigation strategies.

A socially distanced gym class in Provo, Utah.Credit…George Frey/Getty Images
A student entered Joyce Kilmer Elementary in Chicago, where schools are reopening after protracted disagreements with the teachers’ union.Credit…Taylor Glascock for The New York Times

“We need detailed guidance from the C.D.C. that doesn’t leave room for political games,” she said. “This is an airborne disease. Masks must be mandated, social distancing must be in place and proper ventilation is a must.”

As it had previously, the C.D.C. recommended using two measures to determine the risk of transmission in the community: the total number of new cases per 100,000 people, and the percentage of positive test results over the previous seven days.

The agency established four risk levels whose thresholds do not significantly differ from previous recommendations, except that the data are evaluated over seven days instead of 14 — a change that may allow schools to respond more quickly to shifting virus prevalence in their communities.

Dr. Jenkins of Boston University said the percentage of positive tests can vary with how much testing a community is doing. And the highest levels of community spread defined by the agency — 10 percent positivity, and 100 cases per 100,000 people over the previous seven days — are too conservative, she and other experts said.

“I do worry that there might be an impact on unnecessarily delaying the opening for the middle- and high school students,” said Dr. Grupp-Phelan of the University of California, San Francisco.

She added that her hospital, in a region where most middle- and high schools are closed, had seen large increases in adolescents who were suicidal or had developed eating disorders.

President Biden has pledged to open the majority of K-8 schools within the first 100 days of his administration. But on Wednesday, the White House press secretary, Jen Psaki, said that the president had been referring to in-person teaching “at least one day a week.”

That goal is already in reach: A majority of districts are offering at least some in-person learning, and about half the nation’s students are reporting to classrooms. The divide often falls along political lines. Conservative areas are likely to have open schools, while in liberal cities and suburbs, where teachers’ unions are influential, schools are more likely to be operating remotely.

Many districts, particularly ones in the South and the middle of the country, have offered fully in-person instruction for some or all grades at times when virus levels have risen far above what the C.D.C. says is advisable.

According to the agency’s guidelines, the approximately one-third of schools that remain entirely virtual may be too cautious.

Students received hand sanitizer before entering P.S. 316 in Brooklyn in December.Credit…Anna Watts for The New York Times
Temperature checks at Joyce Kilmer Elementary in Chicago on Thursday.Credit…Taylor Glascock for The New York Times

If the new recommendations had been in place last fall, for example, San Francisco could have opened all of its schools for fully in-person instruction in mid-September (although the city may have chosen to close middle- and high schools as cases began climbing in November).

Today, according to the guidelines, San Francisco could open elementary schools in a hybrid mode, and is close to being able to open middle- and high schools in a hybrid mode.

Instead the city’s schools have been shuttered since the pandemic began, and the district has agreed to far more restrictive reopening standards with its union. Officials have set no date for bringing young children back to school, and have said they do not expect most middle- and high school students to return in person this year.

Rebecca Bodenheimer is a mother of a third-grader in Oakland, Calif., and an organizer of a parent group that has been pushing the city’s school district, which is currently all virtual, to set a date for reopening.

The C.D.C.’s guidelines sounded reasonable, Ms. Bodenheimer said. But she was not sure they would sway a debate that was emotional for many.

“The research and data have been piling up about the fact that schools can open safely, and those people who are just only operating on unfounded fear — I don’t see a lot of them coming around,” she said.

Some local unions continue to fight reopening efforts, demanding that teachers be vaccinated before returning to classrooms. The new guidance recommended that states immunize teachers in early phases of the rollout but said access to vaccines should “nevertheless not be considered a condition for reopening schools for in-person instruction.”

Vaccinating teachers is very effective at cutting down cases in both teachers and students in a model of transmission in high schools, said Carl Bergstrom, an infectious diseases expert at the University of Washington in Seattle. “It should be an absolute priority,” he said.

Still, he added, “I can certainly see why they chose not to make it a prerequisite, because it may not be something that can be done in time to have schools open.”

Teachers’ unions have also asked for stringent protections regarding hygiene and air quality inside school buildings.

In Boston, for example, air quality was a major point of contention in reopening negotiations between the school district and teachers’ union. The agreement that paved the way to students returning to schools called for air purifiers in classrooms and a system for testing and reporting air quality data.

Ms. Pringle, the union president, said her members continue to be concerned about aging school buildings that do not include modern ventilation systems. Those schools were more likely to be located in lower-income and nonwhite communities hit hardest by the pandemic.

Many teachers have “no trust” that school administrators will put strong virus safety measures in place or will be given the funding to do so, Ms. Pringle said: “That’s why you see educators rising up across the country and saying, ‘At least give us the vaccine.’”

Covid Vaccines for Kids Are Coming, but Not for Many Months

Covid Vaccines for Kids Are Coming, but Not for Many Months

Pfizer and Moderna are testing their vaccines on children 12 and older and hope to have results by the summer.

A 15-year-old participating in Moderna’s teen Covid vaccine trial received a shot in Houston this month.
A 15-year-old participating in Moderna’s teen Covid vaccine trial received a shot in Houston this month.Credit…Brandon Thibodeaux for The New York Times
Apoorva Mandavilli

  • Feb. 12, 2021, 5:00 a.m. ET

As adults at high risk for Covid-19 line up to be immunized against the coronavirus, many parents want to know: When will my child get a vaccine?

The short answer: Not before late summer.

Pfizer and Moderna have enrolled children 12 and older in clinical trials of their vaccines and hope to have results by the summer. Depending on how the vaccines perform in that age group, the companies may then test them in younger children. The Food and Drug Administration usually takes a few weeks to review data from a clinical trial and authorize a vaccine.

Three other companies — Johnson & Johnson, Novavax and AstraZeneca — also plan to test their vaccines in children, but are further behind.

When researchers test drugs or vaccines in adults first, they typically then move down the age brackets, watching for any changes in the effective dose and for unexpected side effects.

“It would be pretty unusual to start going down into children at an early stage,” said Dr. Emily Erbelding, an infectious diseases physician at the National Institutes of Health who oversees testing of Covid-19 vaccines in special populations.

Some vaccines — those that protect against pneumococcal or meningococcal bacteria or rotavirus, for example — were tested in children first because they prevent pediatric diseases. But it made sense for coronavirus vaccines to be first tested in and authorized for adults because the risk of severe illness and death from Covid-19 increases sharply with age, said Paul Offit, a professor at the University of Pennsylvania and a member of the F.D.A.’s vaccine advisory panel.

“We’re trying to save lives, keep people out of the I.C.U., keep them from dying,” Dr. Offit said. That means prioritizing vaccines for the oldest people and for those with underlying conditions.

People younger than 21 account for about one-quarter of the population in the United States, but they make up less than 1 percent of deaths from Covid-19. Still, about 2 percent of children who get Covid-19 require hospital care, and at least 227 children in the United States have died of the disease.

“It is a significant disease in children, just not necessarily when you compare it to adults,” said Dr. Kristin Oliver, a pediatrician and vaccine expert at Mount Sinai Hospital in New York.

Children will also need to be vaccinated in order for the United States to approach herd immunity — that long-promised goal at which the pandemic slows to a halt because the virus runs out of people to infect.

Scientists have estimated that 70 to 90 percent of the population might need to be immunized against the coronavirus to reach herd immunity, especially with more contagious variants expected to circulate widely in the country.

“Not all adults can get the vaccine because there’s some reluctance, or there’s maybe even some vulnerable immune systems that just don’t respond,” Dr. Erbelding said. “I think we have to include children if we’re going to get to herd immunity.”

It will also be important to immunize children in racial and ethnic populations that are hit hardest by the pandemic, she added.

Abhinav, 12, a participant in the Pfizer vaccine trial at Cincinnati Children’s Hospital last month.
Abhinav, 12, a participant in the Pfizer vaccine trial at Cincinnati Children’s Hospital last month.Credit…Cincinnati Children’s Hospital

Pfizer and Moderna’s clinical trials in adults each enrolled about 50,000 participants. They had to be that large in order to show significant differences between the volunteers who received a vaccine and those who got a placebo. But because it is rarer for children to become seriously ill with Covid-19, that kind of trial design in children would not be feasible, because it would require many more participants to show an effect.

Instead, the companies will look at vaccinated children for signs of a strong immune response that would protect them from the coronavirus.

The Pfizer-BioNTech vaccine was authorized in December for anyone 16 and older. The company has continued its trial with younger volunteers, recruiting 2,259 adolescents from 12 to 15 years of age. Teenagers are roughly twice as likely to be infected with the coronavirus as younger children, according to the Centers for Disease Control and Prevention.

Results from that trial should be available by summer, said Keanna Ghazvini, a spokeswoman for Pfizer.

“Moving below 12 years of age will require a new study and potentially a modified formulation or dosing schedule,” Ms. Ghazvini said. Those trials will most likely start later in the year, but the plans will be made final after the company has data from older children, she added.

Moderna’s vaccine, which was also authorized in December, is on a similar track for pediatric testing. In December, the company began testing adolescents ages 12 through 17, and plans to enroll 3,000 volunteers in this age group. The company expects results “around midyear 2021,” said Colleen Hussey, a spokeswoman for Moderna.

Based on the results, Moderna plans to assess the vaccine later this year in children between the ages of 6 months and 11 years.

Infants may have some antibodies at birth from vaccinated or infected mothers, but that maternal protection is unlikely to last through the first year of age. And with their relatively weak immune systems, babies might be particularly susceptible to infection if community transmission is high.

The trials will also assess the vaccine’s safety in children — and hopefully ease any fears that parents have. One-third of adults in the United States have said they do not plan to have their children immunized against the coronavirus, according to a recent poll conducted by Verywell Health.

Given the low risk of Covid-19 in children, some parents might be skeptical of the urgency to inoculate their children with a brand-new jab, Dr. Offit said. “For that reason, the vaccine would have to be held to a very high standard of safety,” he said.

More than 42 million people in the United States have been immunized so far, with few lasting side effects. And the F.D.A. has set up multiple systems to carefully monitor any serious reactions to the vaccine.

“They’re really looking at the data very, very closely,” Dr. Oliver said. “As a pediatrician and a mom, I have really good confidence that those systems work.”

Once a vaccine for children is available, schools can reintroduce extracurricular activities that involve close contact, like band practice, team sports and choir. But in the meantime, there is ample evidence that schools can reopen with other precautions in place, Dr. Oliver said.

“I don’t think we need to anticipate having a vaccine in order to open schools in the fall,” she said. “We should be planning now for opening schools.”

Dr. Oliver also urged parents to make sure children are immunized for other diseases. According to the C.D.C., orders for non-flu childhood vaccines through the Vaccines for Children Program are down approximately 10.3 million doses over all.

“Now’s the time to really catch up on missed doses of those vaccines,” she said. “Measles, HPV, tetanus boosters, pertussis boosters — all of that is really important.”

Childhood Colds Do Not Prevent Coronavirus Infection, Study Finds

Childhood Colds Do Not Prevent Coronavirus Infection, Study Finds

New research casts doubt on the idea that prior infections with garden-variety coronaviruses might shield some people, particularly children, amid the pandemic.

Drive-through coronavirus antibody testing last month in Los Angeles.
Drive-through coronavirus antibody testing last month in Los Angeles.Credit…Ringo Chiu/Agence France-Presse — Getty Images
Apoorva Mandavilli

  • Feb. 10, 2021, 5:00 a.m. ET

The theory was simple and compelling: Children are less vulnerable to the new coronavirus because they carry antibodies to other common coronaviruses that cause the common cold. The idea might also explain why some people infected with the new virus have mild symptoms while others — presumably without antibodies to common cold coronaviruses — are much more severely affected.

The notion gained traction particularly among people who claimed that this existing protection would swiftly bring human populations to herd immunity, the point at which a pathogen’s spread slows to a halt as it runs out of hosts to infect. A study in the journal Science, published in December, gave the hypothesis a strong boost.

But for all its appeal, the theory does not hold up, according to a new study published on Tuesday in the journal Cell. Based on carefully conducted experiments with live virus and with hundreds of blood samples drawn before and after the pandemic, the new research refutes the idea that antibodies to seasonal coronaviruses have any impact on the new coronavirus, called SARS-CoV-2.

“Going into this study, we thought we would learn that individuals that had pre-existing, pre-pandemic antibodies against SARS-CoV-2 would be less susceptible to infection and have less severe Covid-19 disease,” said Scott Hensley, an immunologist at the University of Pennsylvania. “That’s not what we found.”

He and his colleagues concluded that most people are exposed to seasonal coronaviruses by age 5. As a result, about one in five people carries antibodies that recognize the new coronavirus.

But these antibodies are not neutralizing — they cannot disarm the virus, nor do they mitigate the severity of symptoms following infection, the team found.

The researchers also compared antibodies to common cold coronaviruses in children and adults and found no difference in the amounts. By contrast, the study in Science had reported that about 5 percent of adults carried those antibodies, compared with 43 percent of children.

That study “reported very high levels of pre-pandemic cross-reactive neutralizing antibodies in kids, something that we did not find,” Dr. Hensley said. (“Cross-reactive” refers to antibodies able to attack similar sites on more than one type of virus.)

“I don’t have an explanation for the difference from the Science study, honestly,” he added.

Perhaps the difference in locations — Pennsylvania, in his study, versus Britain in the previous research — may explain some of the discrepancy, he said.

Other experts said they found Dr. Hensley’s study to be more convincing of the two and more consistent with circumstances in which large groups of people become infected with the new coronavirus.

Schoolchildren at the South Boston Catholic Academy in Boston gave themselves Covid-19 tests last month.
Schoolchildren at the South Boston Catholic Academy in Boston gave themselves Covid-19 tests last month.Credit…Allison Dinner/Reuters

For example, a single person infected with the new coronavirus at a Wisconsin summer camp set off an outbreak that affected 76 percent of the other attendees, noted John Moore, a virologist at Weill Cornell Medicine in New York.

Similarly, on a fishing trawler that left for sea from Seattle, only three sailors who had antibodies to the new coronavirus before the trip stayed virus-free. Those are not the infection rates you would see if protective antibodies were widely distributed in the population, Dr. Moore said.

“The idea that having the snuffles a while back somehow protects you from SARS-CoV-2 infection has always left me cold, but it’s been a persistent urban legend throughout the pandemic,” he said. “Hopefully, this new paper will finally cool everyone down and put such thoughts into the freezer.”

Experts also praised the new study’s careful and rigorous approach.

“It’s really nice to have a study that’s this well done,” said Shane Crotty, a virologist at the La Jolla Institute of Immunology in San Diego.

The theory that existing antibodies can protect people from the new virus “has definitely got a strong appeal because at first blush, it can explain a lot of the pandemic,” Dr. Crotty said. “But a beautiful idea doesn’t make it true.”

Dr. Hensley and his colleagues examined samples from 251 people who had donated blood to the University of Pennsylvania before the pandemic and then went on to develop Covid-19.

Those people carried levels of antibodies able to recognize the new coronavirus that were no different from those seen in blood samples drawn from 251 people who remained uninfected. And the levels showed no relationship to the clinical outcome in any of the patients.

“It’s hard to come by those kinds of samples — I was just impressed,” said Marion Pepper, an immunologist at the University of Washington in Seattle. “It’s like three different studies wrapped into one.”

The most important part of the coronavirus is the spike protein on its surface, which docks onto human cells. The spike is also the most distinctive part of the virus, so it makes sense that antibodies to seasonal viruses would be unlikely to recognize and disarm it, Dr. Pepper said.

“There are very specific parts of these viruses that are critical for infection, and most of this cross-reactivity isn’t directed to those parts,” she said.

But George Kassiotis, an immunologist at the Francis Crick Institute in London who led the study published in Science, disagreed with the conclusions of the new research. It “largely confirms rather than contradicts our main findings,” he said, adding that the new study was too small to rule out any role for existing antibodies.

But even if people really were carrying coronavirus antibodies from childhood infections, the protection they confer is not powerful enough to matter, said Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle.

“If there is no effect that is measurable in a study with hundreds of people in both the infected and uninfected groups, then the effect is certainly tiny,” Dr. Bloom said.

Most of the vaccines developed for the new coronavirus are focused on the spike protein. Some scientists have argued that antibodies to other parts of the virus may also be critical to protection. But the new study suggests that the other antibodies are of minimal importance in protecting people from SARS-CoV-2.

The experts all said the new study did not rule out a role for immune cells, called memory B cells and T cells, produced in response to seasonal coronaviruses. Those cells might recognize some parts of the new virus and attack it, easing the severity of symptoms.

Still, the cells would not prevent infection, Dr. Crotty said. When exposed to the new virus, the immune cells might be roused “fast enough that you would have an asymptomatic infection that you never noticed,” he said. “But no, they wouldn’t stop infection.”

Tests of T cells are laborious and expensive, so analyses of their contribution to immunity are not yet complete. In the meantime, the new study at least rules out a significant role for existing antibodies, Dr. Hensley said: “We’ve sort of written one chapter here, but there’s still so much to be learned.”

Weekly Health Quiz: Covid Variants, Moderate Exercise and Coffee

1 of 7

A new variant of coronavirus, first identified in Britain, is spreading through the United States. Which statement about the new variant is not true?

The new variant is much more contagious than earlier forms of the coronavirus

The new variant is much more deadly than earlier forms of the virus

The new variant is expected to be the dominant form of the virus in the United States by March

Scientists believe current vaccines will be effective against the new variant

2 of 7

A new study compared high-intensity interval training with moderate workouts in sedentary, overweight men. Men who did moderate workouts showed this benefit:

They shed more body fat

They showed greater improvements in blood pressure

They were better able to metabolize fats in the diet

All of the above

3 of 7

Robotic-assisted surgery has shown the most gains in replacement of this joint:

Hip

Shoulder

Knee

Elbow

4 of 7

The United States reached a grim milestone in Covid-related deaths, which now exceed:

100,000

200,000

400,000

1 million

5 of 7

Men and women with pain and stiffness from knee arthritis showed the most improvements when they wore shoes that were:

Flat-soled and flexible

Stable, supportive and well-cushioned

Tightly laced with a low, broad heel

The type of footwear had little impact on symptoms of arthritis

6 of 7

Just one alcoholic drink a day was tied to an increased risk of this heart disorder:

Atrial fibrillation

Heart failure

Heart attack

High blood pressure

7 of 7

Men who drank coffee were at lower risk of this condition:

Erectile dysfunction

Prostate cancer

Amyotrophic lateral sclerosis

Dementia

Emerging Coronavirus Variants May Pose Challenges to Vaccines

Emerging Coronavirus Variants May Pose Challenges to Vaccines

Laboratory studies of mutations circulating in South Africa suggest they may dodge some of the body’s immune responses.

Health workers tended to a Covid-19 patient at Greenacres Hospital in Port Elizabeth, South Africa, in November.
Health workers tended to a Covid-19 patient at Greenacres Hospital in Port Elizabeth, South Africa, in November.Credit…Samantha Reinders for The New York Times
Apoorva Mandavilli

  • Jan. 20, 2021, 6:37 p.m. ET

The steady drumbeat of reports about new variants of the coronavirus — first in Britain, then in South Africa, Brazil and the United States — have brought a new worry: Will vaccines protect against these altered versions of the virus?

The answer so far is yes, several experts said in interviews. But two small new studies, posted online Tuesday night, suggest that some variants may pose unexpected challenges to the immune system, even in those who have been vaccinated — a development that most scientists had not anticipated seeing for months, even years.

The findings result from laboratory experiments with blood samples from groups of patients, not observations of the virus spreading in the real world. The studies have not yet been peer-reviewed.

But experts who reviewed the papers agreed that the findings raised two disturbing possibilities. People who had survived mild infections with the coronavirus may still be vulnerable to infection with a new variant; and more worryingly, the vaccines may be less effective against the variants.

Existing vaccines will still prevent serious illness, and people should continue getting them, said Dr. Michel Nussenzweig, an immunologist at Rockefeller University in New York, who led one of the studies: “If your goal is to keep people out of the hospital, then this is going to work just fine.”

But the vaccines may not prevent people from becoming mildly or asymptomatically infected with the variants, he said. “They may not even know that they were infected,” Dr. Nussenzweig added. If the infected can still transmit the virus to others who are not immunized, it will continue to claim lives.

The vaccines work by stimulating the body to produce antibodies against the coronavirus. Scientists had expected that over time, the virus may gain mutations that allow it to evade these antibodies — so-called escape mutations. Some studies had even predicted which mutations would be most advantageous to the virus.

But scientists had hoped that the new vaccines would remain effective for years, on the theory that the coronavirus would be slow to develop new defenses against them. Now some researchers fear the unchecked spread has given the virus nearly unfettered opportunities to reinvent itself, and may have hastened the appearance of escape mutations.

The studies published on Tuesday night show that the variant identified in South Africa is less susceptible to the antibodies created by natural infection and by vaccines made by Pfizer-BioNTech and Moderna.

Vaccinations of nurses, doctors and health professionals in São Paulo, Brazil, this week.
Vaccinations of nurses, doctors and health professionals in São Paulo, Brazil, this week.Credit…Victor Moriyama for The New York Times

Neither the South African variant nor a similar mutant virus in Brazil has yet been detected in the United States. (The more contagious variant that has blazed through Britain does not contain these mutations and seems to be susceptible to vaccines.)

Fears that the vaccines would be powerless against new variants intensified at a scientific conference held online on Saturday, when South African scientists reported that in laboratory tests, serum samples from 21 of a group of 44 Covid-19 survivors did not destroy the variant circulating in that country.

The samples that were successful against the variant were taken from patients who had been hospitalized. These patients had higher blood levels of so-called neutralizing antibodies — the subset of antibodies needed to disarm the virus and prevent infection — than those who were only mildly ill.

The results “strongly, strongly suggest that several mutations that we see in the South Africa variant are going to have a significant effect on the sensitivity of that virus to neutralization,” said Penny Moore, a virologist at the National Institute for Communicable Diseases in South Africa who led the study.

The second study brought better tidings, at least about vaccines.

In that study, Dr. Nussenzweig and his colleagues tested samples from 14 people who had received the Moderna vaccine and six people who had received the Pfizer-BioNTech vaccine.


Covid-19 Vaccines ›


Answers to Your Vaccine Questions

While the exact order of vaccine recipients may vary by state, most will likely put medical workers and residents of long-term care facilities first. If you want to understand how this decision is getting made, this article will help.

Life will return to normal only when society as a whole gains enough protection against the coronavirus. Once countries authorize a vaccine, they’ll only be able to vaccinate a few percent of their citizens at most in the first couple months. The unvaccinated majority will still remain vulnerable to getting infected. A growing number of coronavirus vaccines are showing robust protection against becoming sick. But it’s also possible for people to spread the virus without even knowing they’re infected because they experience only mild symptoms or none at all. Scientists don’t yet know if the vaccines also block the transmission of the coronavirus. So for the time being, even vaccinated people will need to wear masks, avoid indoor crowds, and so on. Once enough people get vaccinated, it will become very difficult for the coronavirus to find vulnerable people to infect. Depending on how quickly we as a society achieve that goal, life might start approaching something like normal by the fall 2021.

Yes, but not forever. The two vaccines that will potentially get authorized this month clearly protect people from getting sick with Covid-19. But the clinical trials that delivered these results were not designed to determine whether vaccinated people could still spread the coronavirus without developing symptoms. That remains a possibility. We know that people who are naturally infected by the coronavirus can spread it while they’re not experiencing any cough or other symptoms. Researchers will be intensely studying this question as the vaccines roll out. In the meantime, even vaccinated people will need to think of themselves as possible spreaders.

The Pfizer and BioNTech vaccine is delivered as a shot in the arm, like other typical vaccines. The injection won’t be any different from ones you’ve gotten before. Tens of thousands of people have already received the vaccines, and none of them have reported any serious health problems. But some of them have felt short-lived discomfort, including aches and flu-like symptoms that typically last a day. It’s possible that people may need to plan to take a day off work or school after the second shot. While these experiences aren’t pleasant, they are a good sign: they are the result of your own immune system encountering the vaccine and mounting a potent response that will provide long-lasting immunity.

No. The vaccines from Moderna and Pfizer use a genetic molecule to prime the immune system. That molecule, known as mRNA, is eventually destroyed by the body. The mRNA is packaged in an oily bubble that can fuse to a cell, allowing the molecule to slip in. The cell uses the mRNA to make proteins from the coronavirus, which can stimulate the immune system. At any moment, each of our cells may contain hundreds of thousands of mRNA molecules, which they produce in order to make proteins of their own. Once those proteins are made, our cells then shred the mRNA with special enzymes. The mRNA molecules our cells make can only survive a matter of minutes. The mRNA in vaccines is engineered to withstand the cell’s enzymes a bit longer, so that the cells can make extra virus proteins and prompt a stronger immune response. But the mRNA can only last for a few days at most before they are destroyed.

The researchers saw a slight decrease in antibody activity directed against engineered viruses with three of the key mutations in the variant identified in South Africa. That result was significant “because it’s seen in just about every individual tested,” Dr. Nussenzweig said. Still, it “is not something that we should be horribly freaked out about.”

In most people, infection with the coronavirus leads to a strong immune response; the vaccines seem to induce an even more powerful response. Two doses of the vaccines from Pfizer and Moderna, at least, produce neutralizing antibodies at levels that are higher than those acquired through natural infection.

Even if antibody effectiveness were reduced tenfold, the vaccines would still be quite effective against the virus, said Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle.

In Liverpool, England, people lined up to receive a coronavirus test at a recreational tennis center last year.Credit…Mary Turner for The New York Times

And while neutralizing antibodies are essential for preventing infection, the vaccines — and natural infection — also lead to production of thousands of other types of antibodies, not to mention various immune cells that retain a memory of the virus and can be roused to action when the body encounters it again.

Even when confronted with variants, those other components of the immune system may be enough to prevent serious illness, said Florian Krammer, an immunologist at the Icahn School of Medicine at Mount Sinai in New York. In clinical trials, the vaccines protected people from illness after just one dose, when the levels of neutralizing antibodies were low or undetectable, he noted.

Vaccine trials being conducted in South Africa by Novavax and Johnson & Johnson will provide more real-world data on how the vaccines perform against the new variant there. Those results are expected within the next few weeks.

All viruses mutate, and it’s no surprise that some of those mutations sidestep the body’s immune defenses, experts said. Each new host affords a virus fresh opportunities to amass and test mutations by slightly scrambling the sequence of RNA letters in its genetic code.

“The beauty, the elegance, the evolution and the magnificence of a virus is that every single time it infects a person, it’s exploring that sequence space,” said Paul Duprex, director of the Center for Vaccine Research at the University of Pittsburgh.

Some mutations don’t improve on the original, and fade away. Others add to the pathogen’s power, by making it more contagious — like the variant first identified in Britain — more fit, or less susceptible to immunity.

The mutations in the variant circulating in South Africa, called B.1.351, have independently emerged more than once, and all together, suggesting that they work in concert to benefit the virus.

A field hospital for treating Covid-19 patients outside Port Elizabeth, South Africa, in November. Credit…Samantha Reinders for The New York Times

The key mutation, called E484K, and two of its companions alter the shape of a part of the virus that is crucial for immune recognition, making it difficult for antibodies to attach themselves to the virus. The trio popped up in several lab studies that tried to predict which mutations would be advantageous to the virus.

“I think we need to monitor mutations closely and look out for things like that that could be becoming dominant in certain parts of the world,” said Akiko Iwasaki, an immunologist at Yale University.

Britain detected the more contagious variant circulating there because it sequences more virus samples than any other nation. The United States lags far behind: It has sequenced about 71,000 samples so far, a tiny proportion of the millions infected in the country. But the Centers for Disease Control and Prevention plans to work with state and local public health labs to sequence as many as 6,000 samples per week, agency scientists said Friday.

It will be important to limit travel — and the import of variants — from other countries until a majority of the population is immunized, said John Moore, a virologist at Weill Cornell Medicine in New York.

“Even if they are already here, the more often they are reintroduced, the more likely there could be a super-spreader event,” Dr. Moore said. (President Joseph R. Biden Jr. plans to sustain existing travel restrictions on anyone who has recently traveled to Europe and Brazil.)

The mRNA technology on which the Pfizer and Moderna vaccines rely can be altered in a matter of weeks, and far more easily than the process used to produce flu vaccines. But it would be wise to prepare for this eventuality now and think through not just the technical aspects of updating the vaccines, but the testing, approval and rollout of those vaccines, experts said.

Still, the best path forward is to prevent the emergence of new mutations and variants altogether, they said.

“Imagine having to do catch-up like this all the time — it’s not something desirable,” Dr. Iwasaki said. “If we can just stop the spread as soon as possible, while the vaccine is very effective, that’s the best way.”

What You Can Do to Avoid the New Coronavirus Variant Right Now

Ask Well

What You Can Do to Avoid the New Coronavirus Variant Right Now

It’s more contagious than the original and spreading quickly. Upgrade your mask and double down on precautions to protect yourself.

Credit…Getty Images
Tara Parker-Pope

  • Jan. 19, 2021Updated 3:44 p.m. ET

New variants of the coronavirus continue to emerge. But one in particular has caused concern in the United States because it’s so contagious and spreading fast. To avoid it, you’ll need to double down on the same pandemic precautions that have kept you safe so far.

The variant known as B.1.1.7., which was first identified in Britain, doesn’t appear to cause more severe disease, but it has the potential to infect an estimated 50 percent more people. The Centers for Disease Control and Prevention has predicted that this variant could become the dominant source of infection in the United States by March. Variants with the same mutation have been reported in Brazil and South Africa, and now scientists are studying whether a variant with a different mutation, and first found in Denmark, has caused a surge in cases in California.

The new variant spreading in the United States appears to latch onto our cells more efficiently. (You can find a detailed look inside the variant here.) The change suggests it could take less virus and less time in the same room with an infected person for someone to become ill. People infected with the variant may also shed larger quantities of virus, which increases the risk to people around them.

“The exact mechanism in which it’s more transmissible isn’t entirely known,” said Nathan D. Grubaugh, assistant professor and epidemiologist at the Yale School of Public Health. “It might just be that when you’re infected, you’re exhaling more infectious virus.”

So how do you avoid a more-contagious version of the coronavirus? I spoke with some of the leading virus and infectious disease experts about what makes the new variant so worrisome and what we can do about it. Here’s what they had to say.

How can I protect myself from the new coronavirus variant?

The variant spreads the same way the coronavirus has always spread. You’re most likely to contract the virus if you spend time in an enclosed space breathing the air of an infected person. The same things that have protected you from the original strain should help protect you from the variant, although you may need to be more rigorous. Wear a two- or three-layer mask. Don’t spend time indoors with people not from your household. Avoid crowds, and keep your distance. Wash your hands often, and avoid touching your face.

“The first thing I say to people is that it’s not a different virus. All the things we have learned about this virus still apply,” said Dr. Ashish K. Jha, dean of the Brown University School of Public Health. “It’s not like this variant is somehow magically spreading through other means. Anything risky under the normal strain just becomes riskier with the variant.”

And let’s face it, after months of pandemic living, many of us have become lax about our Covid safety precautions. Maybe you’ve let down your guard, and you’re spending time indoors and unmasked with trusted friends. Or perhaps you’ve been dining in restaurants or making more trips to the grocery store each week than you did at the start of lockdowns. The arrival of the variant means you should try to cut back on potential exposures where you can and double down on basic precautions for the next few months until you and the people around you get vaccinated.

“The more I hear about the new variants, the more concerned I am,” said Linsey Marr, professor of civil and environmental engineering at Virginia Tech and one of the world’s leading aerosol scientists. “I think there is no room for error or sloppiness in following precautions, whereas before, we might have been able to get away with letting one slide.”

Should I upgrade my mask?

You should be wearing a high-quality mask when you run errands, go shopping or find yourself in a situation where you’re spending time indoors with people who don’t live with you, Dr. Marr said. “I am now wearing my best mask when I go to the grocery store,” she said. “The last thing I want to do is get Covid-19 in the month before I get vaccinated.”

Dr. Marr’s lab recently tested 11 mask materials and found that the right cloth mask, properly fitted, does a good job of filtering viral particles of the size most likely to cause infection. The best mask has three layers — two cloth layers with a filter sandwiched in between. Masks should be fitted around the bridge of the nose and made of flexible material to reduce gaps. Head ties create a better fit than ear loops.


Covid-19 Vaccines ›


Answers to Your Vaccine Questions

While the exact order of vaccine recipients may vary by state, most will likely put medical workers and residents of long-term care facilities first. If you want to understand how this decision is getting made, this article will help.

Life will return to normal only when society as a whole gains enough protection against the coronavirus. Once countries authorize a vaccine, they’ll only be able to vaccinate a few percent of their citizens at most in the first couple months. The unvaccinated majority will still remain vulnerable to getting infected. A growing number of coronavirus vaccines are showing robust protection against becoming sick. But it’s also possible for people to spread the virus without even knowing they’re infected because they experience only mild symptoms or none at all. Scientists don’t yet know if the vaccines also block the transmission of the coronavirus. So for the time being, even vaccinated people will need to wear masks, avoid indoor crowds, and so on. Once enough people get vaccinated, it will become very difficult for the coronavirus to find vulnerable people to infect. Depending on how quickly we as a society achieve that goal, life might start approaching something like normal by the fall 2021.

Yes, but not forever. The two vaccines that will potentially get authorized this month clearly protect people from getting sick with Covid-19. But the clinical trials that delivered these results were not designed to determine whether vaccinated people could still spread the coronavirus without developing symptoms. That remains a possibility. We know that people who are naturally infected by the coronavirus can spread it while they’re not experiencing any cough or other symptoms. Researchers will be intensely studying this question as the vaccines roll out. In the meantime, even vaccinated people will need to think of themselves as possible spreaders.

The Pfizer and BioNTech vaccine is delivered as a shot in the arm, like other typical vaccines. The injection won’t be any different from ones you’ve gotten before. Tens of thousands of people have already received the vaccines, and none of them have reported any serious health problems. But some of them have felt short-lived discomfort, including aches and flu-like symptoms that typically last a day. It’s possible that people may need to plan to take a day off work or school after the second shot. While these experiences aren’t pleasant, they are a good sign: they are the result of your own immune system encountering the vaccine and mounting a potent response that will provide long-lasting immunity.

No. The vaccines from Moderna and Pfizer use a genetic molecule to prime the immune system. That molecule, known as mRNA, is eventually destroyed by the body. The mRNA is packaged in an oily bubble that can fuse to a cell, allowing the molecule to slip in. The cell uses the mRNA to make proteins from the coronavirus, which can stimulate the immune system. At any moment, each of our cells may contain hundreds of thousands of mRNA molecules, which they produce in order to make proteins of their own. Once those proteins are made, our cells then shred the mRNA with special enzymes. The mRNA molecules our cells make can only survive a matter of minutes. The mRNA in vaccines is engineered to withstand the cell’s enzymes a bit longer, so that the cells can make extra virus proteins and prompt a stronger immune response. But the mRNA can only last for a few days at most before they are destroyed.

If you don’t want to buy a new mask, a simple solution is to wear an additional mask when you find yourself in closer proximity to strangers. I wear a single mask when I walk my dog or exercise outdoors. But if I’m going to a store, taking a taxi or getting in the subway, I double mask by using a disposable surgical mask and covering it with my cloth mask.

Do I need an N95 medical mask?

While medical workers who come into close contact with sick patients rely on the gold-standard N95 masks, you don’t need that level of protection if you’re avoiding group gatherings, limiting shopping trips and keeping your distance from others.

“N95s are hard to get,” said Dr. Jha. “I don’t think people should think that’s what they need. Certainly there are a lot of masks out in the marketplace that are pretty good.”

If you’re working in an office or grocery store, or find yourself in a situation where you want added mask protection, you can get an alternative to the N95. Dr. Jha suggested using a KF94 mask, a type of mask made in South Korea that can be purchased easily online. It resembles an N95, with some differences. It’s made of a similar nonwoven material that blocks 94 percent of the hardest-to-trap viral particles. But the KF94 has ear loops, instead of elastic head bands, so it won’t fit as snugly as an N95.

The KF94 is also disposable — you can buy a pack of 20 for about $40 on Amazon. While you can let a KF94 mask air dry and reuse it a few times, it can’t be laundered and won’t last as long as a cloth mask. One solution is to save your KF94 mask for higher risk situations — like riding a subway, spending time in a store or going to a doctor’s appointment. Use your cloth mask for outdoor errands, exercise or walking the dog.

Are there additional ways to reduce my risk?

Getting the vaccine is the ultimate way to reduce risk. But until then, take a look at your activities and try reducing the time and number of exposures to other people.

For instance, if you now go to the store two or three times a week, cut back to just once a week. If you’ve been spending 30 to 45 minutes in the grocery store, cut your time down to 15 or 20 minutes. If the store is crowded, come back later. If you’re waiting in line, be mindful of staying at least six feet apart from the people ahead of you and behind you. Try delivery or curbside pickup, if that’s an option for you.

If you’ve been spending time indoors with other people who aren’t from your household, consider skipping those events until you and your friends get vaccinated. If you must spend time with others, wear your best mask, make sure the space is well ventilated (open windows and doors) and keep the visit as short as possible. It’s still safest to take your social plans outdoors. And if you are thinking about air travel, it’s a good idea to reschedule given the high number of cases around the country and the emergence of the more contagious variant.

“The new variants are making me think twice about my plan to teach in-person, which would have been with masks and with good ventilation anyway,” Dr. Marr said. “They’re making me think twice about getting on an airplane.”

Will the current Covid vaccines work against the new variants?

Experts are cautiously optimistic that the current generation of vaccines will be mostly effective against the emerging coronavirus variants. Earlier this month, Pfizer and BioNTech announced that their Covid vaccine works against one of the key mutations present in some of the variants. That’s good news, but the variants have other potentially risky mutations that haven’t been studied yet.

Some data also suggest that variants with certain mutations may be more resistant to the vaccines, but far more study is needed and those variants haven’t yet been detected in the United States. While the data are concerning, experts said the current vaccines generate extremely high levels of antibodies, and they are likely to at least prevent serious illness in people who are immunized and get infected.

“The reason why I’m cautiously optimistic is that from what we know about how vaccines work, it’s not just one antibody that provides all the protection,” said Dr. Adam Lauring, associate professor of infectious disease at the University of Michigan. “When you get vaccinated you generate antibodies all over the spike protein. That makes it less likely that one mutation here or there is going to leave you completely unprotected. That’s what gives me reason for optimism that this is going to be OK in terms of the vaccine, but there’s more work to be done.”

If I catch Covid-19, will I know if I have the new variant?

Probably not. If you test positive for Covid-19, the standard PCR test can’t definitively determine if you have the variant or the original strain. While some PCR test results can signal if a person is likely to be infected with a variant, that information probably won’t be shared with patients. The only way to know for sure which variant is circulating is to use gene sequencing technology, but that technology is not used to alert individuals of their status. While some public health and university laboratories are using genomic surveillance to track the prevalence of variants in a community, the United States doesn’t yet have a large-scale, nationwide system for checking coronavirus genomes for new mutations.

Treatment for Covid-19 is the same whether you have the original strain or the variant. You can read more about what to do if you get infected here.

Are children more at risk from the new variant?

Children appear to get infected with the variant at about the same rate as the original strain. A large study by health officials in Britain found that young children are only about half as likely as adults to transmit the variant to others. While that’s good news, the highly contagious nature of the variant means more children will get the virus, even if they are still proportionately less contagious and less prone to getting infected than adults. You can learn more here.

If I’ve already had Covid-19, am I likely to have the same level of immunity to the new strain?

Most experts agree that once you’ve had Covid-19, your body has some level of natural immunity to help fight off a second infection — although it’s not known how long the protection lasts. The variants circulating in Brazil and South Africa appear to have mutations that allow the virus to evade natural antibodies and reinfect someone who has already had the virus. The concern is based on lab tests using antibodies of people with a previous infection, so whether that translates to more reinfections in the real world isn’t known. The effect of the vaccine against these variants isn’t known yet either. While all of this sounds frightening, scientists are hopeful that even if the vaccines don’t fully protect against new variations of the virus, the antibodies generated by the vaccine still will protect people from more serious illness.

What Does a More Contagious Virus Mean for Schools?

What Does a More Contagious Virus Mean for Schools?

The coronavirus variant discovered in Britain is more easily spread among children, as it is among adults. Current safeguards should protect schools, experts said, but only if strictly enforced.

Children in Knutsford, England, returning to school this month following a Christmas break.
Children in Knutsford, England, returning to school this month following a Christmas break.Credit…Martin Rickett/PAMPC, via Associated Press
Apoorva Mandavilli

  • Jan. 14, 2021, 3:46 p.m. ET

It wasn’t until last fall that many parents started to breathe easier, as it became clear that elementary schools, at least, were not cesspools of infection with the coronavirus. But the alarming news of a more contagious version of the virus, first identified in Britain, revived those concerns.

Initial reports were tinged with worry that children might be just as susceptible as adults, fueling speculation that schools might need to pre-emptively close to limit the variant’s spread. But recent research from Public Health England may put those fears to rest.

Based on detailed contact-tracing of about 20,000 people infected with the new variant — including nearly 3,000 children under 10 — the report showed that young children were about half as likely as adults to transmit the variant to others. That was true of the previous iteration of the virus, as well.

“There was a lot of speculation at the beginning suggesting that children spread this variant more,” said Muge Cevik, an infectious disease expert at the University of St. Andrews in Scotland and a scientific adviser to the British government. “That’s really not the case.”

But the variant does spread more easily among children, just as it does among adults. The report estimated that the new variant is about 30 percent to 50 percent more contagious than its predecessors — less than the 70 percent researchers had initially estimated, but high enough that the variant is expected to pummel the United States and other countries, as it did Britain.

Prime Minister Boris Johnson of Britain had promised last year to do all he could to keep schools open. But he changed course in the face of soaring infections and buckling hospital systems, and ordered schools and colleges to move to remote learning. Other European countries put a premium on opening schools in September and have worked to keep them open, though the variant already has forced some to close.

In the United States, the mutant virus has been spotted only in a handful of states but is expected to spread swiftly, becoming the predominant source of infections by March. If community prevalence rises to unmanageable levels — a likely proposition, given the surge in most states — even elementary schools may be forced to close.

But that should be a last resort, after closures of indoor restaurants, bars, bowling alleys and malls, several experts said.

“I still say exactly what many people have said for the past few months — that schools should be the last thing to close,” said Helen Jenkins, an infectious disease expert at Boston University. Keeping schools open carries some risk, but “I think it can be reduced substantially with all the mitigations in place,” she said.

Reports of the new variant first surfaced in early December, and some researchers initially suggested that unlike with previous versions of the virus, children might be just as susceptible to the new variant as adults.

Researchers at P.H.E. looked at how efficiently people of various ages transmitted the variant to others. They found that children under 10 were roughly half as likely as adults to spread the variant.

Adolescents and teenagers between ages 10 and 19 were more likely than younger children to spread the variant, but not as likely as adults. (The range for the older group in the study is too broad to be useful for drawing conclusions, Dr. Cevik said. Biologically, a 10-year-old is very different from a 19-year-old.)

Over all, though, the variant was more contagious in each age group than previous versions of the virus. The mutant virus will result in more infections in children unless schools shore up their precautions, experts said.

“The variant is not necessarily affecting children particularly, but we know that it’s adding on more transmissibility to all age groups,” Dr. Cevik said. “We need to find ways to return these kids back to school as soon as possible; we need to use this time period to prepare.”

A schoolyard in Dortmund, Germany, this month. Fears of the new variant prompted Chancellor Angel Merkel to order schools closed.
A schoolyard in Dortmund, Germany, this month. Fears of the new variant prompted Chancellor Angel Merkel to order schools closed.Credit…Ina Fassbender/Agence France-Presse — Getty Images

In Germany, Chancellor Angela Merkel had vowed that schools would be the last thing to close during the second lockdown that began in November. Schools went to great lengths to keep in-person classes in session, requiring children to wear masks and opening windows to ensure better ventilation even as temperatures plummeted.

But fear of the variant’s spread prompted Ms. Merkel to keep schools closed following the holiday break at least through the end of January.

In France, where the new variant has not resulted in a surge of infections so far, schools reopened earlier this month after the winter break. France was not dealing with a particularly difficult epidemic, and health protocols put in place last September limited transmission in schools, Jean-Michel Blanquer, France’s education minister, has said.

The Italian government, too, has allowed not just elementary schools to open but also high schools, albeit at half capacity. Still, local leaders have implemented tighter restrictions, with some high schools slated to stay closed until the end of the month.

In the United States, the variant has only been spotted in a handful of states, and still accounts for less than 0.5 percent of infections. Schools remain open in New York City and many other parts of the country, but some have had to shut down because of rising virus infections in the community.

“Obviously, we don’t want to get to a point where it seems like we closed schools too late,” said Dr. Uché Blackstock, an urgent care physician in Brooklyn and founder of Advancing Health Equity, a health care advocacy group. “But at the same time, I think that we should try to keep our young children in school for as long as possible for in-person learning.”

It’s been clear for months what measures are necessary, Dr. Blackstock and other experts said: requiring masks for all children and staff; ensuring adequate ventilation in schools, even if just by opening windows or teaching outdoors; maintaining distance between students, perhaps by adopting hybrid schedules; and hand hygiene.

The new variant, while more contagious, is still thwarted by these measures. But only a few schools in Britain implemented them.

“When we look at what’s happened in the U.K. and think about this new variant, and we see all the case numbers going up, we have to remember it in the context of schools being open with virtually no modification at all,” Dr. Jenkins said. “I would like to see a real-life example of that kind of country or state or location, which has managed to control things in schools.”

There are some examples within the United States.

Erin Bromage, an immunologist at the University of Massachusetts Dartmouth, advised the governor of Rhode Island, as well as schools in southern Massachusetts, on preventive measures needed to turn back the coronavirus. The schools that closely adhered to the guidelines have not seen many infections, even when the virus was circulating at high levels in the community, Dr. Bromage said.

“When the system is designed correctly and we’re bringing children into school, they are as safe, if not safer, than they would be in a hybrid or remote system,” he said.

The school Dr. Bromage’s children attend took additional precautions. For example, administrators closed the school a few days before Thanksgiving to lower the risk at family gatherings, and operated remotely the week following the holiday.

Officials tested the nearly 300 students and staff at the end of that week, found only two cases, and decided to reopen.

“That gave us the confidence that our population was not representative of what we were seeing in the wider community,” he said. “We were using data to determine coming back together.”

The tests cost $61 per child, but schools that cannot afford it could consider testing only teachers, he added, because the data suggest the virus is “more likely to move from teacher to teacher than it is from student to teacher.”

In New York City, students and teachers are randomly tested, and have so far shown remarkably low rates of transmission within schools.

Dr. Blackstock has two children at an elementary school in Brooklyn, and said her son has not been tested all year. Even if the new variant brings a spike in cases, the city’s policy of closing a school if it has two unrelated infections is “too conservative,” she said.

If the number of cases skyrockets and the schools shut down more often, “then I would probably say, ‘This doesn’t feel right, let’s keep them home,’” she said. “But they’re going to be in school as long as I can possibly keep them.”

Emma Bubola contributed reporting from Milan, Melissa Eddy from Berlin, Constant Méheut from Paris and Benjamin Mueller from London.

A Riot Amid a Pandemic: Did the Virus, Too, Storm the Capitol?

A Riot Amid a Pandemic: Did the Virus, Too, Storm the Capitol?

Some scientists fear that the mayhem on Capitol Hill may have led to a so-called super-spreading event.

The rally on the National Mall before a mob entered the Capitol on Wednesday.
The rally on the National Mall before a mob entered the Capitol on Wednesday.Credit…Pete Marovich for The New York Times
Apoorva Mandavilli

  • Jan. 7, 2021, 3:29 p.m. ET

The mob that stormed the Capitol yesterday did not just threaten the heart of American democracy. To scientists who watched dismayed as the scenes unfolded on television, the throngs of unmasked intruders who wandered through hallways and into private offices may also have transformed the riot into a super-spreader event.

The coronavirus thrives indoors, particularly in crowded spaces, lingering in the air in tiny particles called aerosols. If even a few extremists were infected — likely, given the current rates of spread and the crowd size — then the virus would have had the ideal opportunity to find new victims, experts said.

“It has all the elements of what we warn people about,” said Anne Rimoin, an epidemiologist at the University of California, Los Angeles. “People yelling and screaming, chanting, exerting themselves — all of those things provide opportunity for the virus to spread, and this virus takes those opportunities.”

President Trump has downplayed the pandemic almost since its beginning, and many of his supporters who entered the Capitol yesterday did not appear to be wearing masks or making any effort at social distancing. Under similar conditions, gatherings held in such close quarters have led to fast-spreading clusters of infection.

But transmission of the virus has always been difficult to track. There is little effective contact tracing in the United States, and many in the crowd at the Capitol arrived from communities far from Washington.

The Black Lives Matter protests in the summer raised similar concerns. But most were held outdoors, and greater numbers of participants seemed to be masked. Research afterward suggested these were not super-spreading events.

Attendees of the rally preceding the rush to the Capitol on Wednesday also stood outdoors close together for hours, but “I’m less worried about what was happening outdoors,” Dr. Rimoin said. “The risk increases exponentially indoors.”

Rioters in the National Statuary Hall in the Capitol on Wednesday.
Rioters in the National Statuary Hall in the Capitol on Wednesday.Credit…Anna Moneymaker for The New York Times

Hundreds of rioters shouting in crowded rooms and hallways for extended periods of time can infect dozens of people at once, she and other experts said.

Three distinct groups — Capitol Police, rioters and members of Congress — “were spending time indoors, without social distancing, for long periods of time,” said Dr. Joshua Barocas, an infectious diseases physician at Boston University. The melee likely was a super-spreader event, he added, “especially given the backdrop of the highly transmissible variants that are circulating.”

Dr. Barocas was referring to a highly contagious new variant of the coronavirus, first identified in Britain. It has been spotted in several U.S. states but may well have spread everywhere in the country, making events like the Capitol riot even more risky, he said.

The idea that members of Congress may have been exposed, amid an already difficult transfer of power, particularly disturbed some scientists. “I am worried not only that it could it could lead to super spreading, but also super spreading to people who are elected officials,” said Dr. Tom Ingelsby, director of the Center for Health Security at Johns Hopkins University.

And infected members of Congress and law enforcement could have spread the virus to one another as they sheltered from the violence, he noted.

Rep. Jake LaTurner, Republican of Kansas, announced on Twitter early Thursday morning that he had tested positive for the virus. Mr. LaTurner was cloistered in the chamber with other members of Congress for much of the day.

At least a dozen of the 400 or so lawmakers and staff who were huddling in one committee room refused to wear masks even after being offered one, or wore them improperly below their chins, said Representative Susan Wild, Democrat of Pennsylvania.

They gathered in a committee room that quickly became crowded, making social distancing impossible, she said. Some of the lawmakers were unmasked, and several were shouting: “Tensions were high, and people were yelling at each other.”

“I just started getting really kind of angry, thinking about the holidays just passed, and how so many people did not spend time with their immediate families for fear of spreading,” she added, referring to her unmasked colleagues.

Representative Debbie Dingell, Democrat of Michigan, said the environment made her so nervous she sat on the floor at one point, hoping to duck whatever virus might be floating about. She has asked experts whether the lawmakers present should now quarantine, she said. She was wearing two masks, as she often does.

“I get that they think they have their individual freedoms,” she said of Republican lawmakers who eschewed masks. “It’s a rule for a reason. It’s to protect the common good.”

Electoral College votes were returned to a joint session of Congress late Wednesday.Credit…Erin Schaff/The New York Times

The risk for members of Congress will depend greatly on ventilation in the room where they sheltered, said Joseph Allen, an expert on buildings quality at the Harvard T.H. Chan School of Public Health in Boston.

“If there is a well-designed secure facility, then it would have great ventilation and filtration,” Dr. Allen said. “If it’s a place where they were just hunkered down wherever they could go that was safe, and it was not a place that was designed like that, then we don’t really know.”

It’s natural in a heart-pounding crisis to disregard risks that seem intangible or theoretical, he and other scientists noted.

“You cannot keep distance if you’re trying to leave a very intense and dangerous situation,” said Seema Lakdawala, an expert in respiratory virus transmission at the University of Pittsburgh. “You’re weighing the risk of your life over the risk of getting a virus at that moment.”

Members of Congress returned to continue the electoral count after the rioters were cleared from the Capitol. Some legislators took off their masks before giving a speech, Dr. Barocas noted, at precisely the time they needed to wear them. Talking at a high volume can expel vast quantities of aerosols, propelling them through an enclosed space.

Scientists have documented infectious aerosols suspended in air nearly 20 feet from an infected person. And a recent study from South Korea found that two people had become infected after spending just five minutes in a restaurant, 15 feet away from an infected patron.

Many Americans breathed sighs of relief as rioters departed the Capitol. Some experts feared that rioters heading back home could set off new chains of infection, perhaps impossible to track.

“We might get an inkling into how bad it might be because of the federal employees,” Dr. Barocas said. But “I don’t think that we’re going to know the extent of this super-spreader event.”

Even as the mob stormed the Capitol on Wednesday, the pandemic marked a grim milestone: The virus claimed nearly 4,000 lives, the highest daily toll thus far. The numbers are expected to keep rising.

The president has “created a culture in which people think it’s a hoax, and these basic control measures are being flouted repeatedly everywhere,” Dr. Allen said.

How Does the Coronavirus Variant Spread? Here’s What Scientists Know

How Does the Coronavirus Variant Spread? Here’s What Scientists Know

Contagiousness is the hallmark of the mutated virus surfacing in the U.S. and more than a dozen other countries.

The first infection with the new variant in the United States was traced to a National Guardsman who was working at the Good Samaritan Society, an assisted living facility in Simla, Calif.
The first infection with the new variant in the United States was traced to a National Guardsman who was working at the Good Samaritan Society, an assisted living facility in Simla, Calif.Credit…Matthew Staver for The New York Times
Apoorva Mandavilli

  • Dec. 31, 2020, 3:37 p.m. ET

A more contagious form of the coronavirus has begun circulating in the United States.

In Britain, where it was first identified, the new variant became the predominant form of the coronavirus in just three months, accelerating that nation’s surge and filling its hospitals. It may do the same in the United States, exacerbating an unrelenting rise in deaths and overwhelming the already strained health care system, experts warned.

A variant that spreads more easily also means that people will need to religiously adhere to precautions like social distancing, mask-wearing, hand hygiene and improved ventilation — unwelcome news to many Americans already chafing against restrictions.

“The bottom line is that anything we do to reduce transmission will reduce transmission of any variants, including this one,” said Angela Rasmussen, a virologist affiliated with Georgetown University. But “it may mean that the more targeted measures that are not like a full lockdown won’t be as effective.”

What does it mean for this variant to be more transmissible? What makes this variant more contagious than previous iterations of the virus? And why should we worry about a variant that spreads more easily but does not seem to make anyone sicker?

We asked experts to weigh in on the evolving research into this new version of the coronavirus.

The new variant seems to spread more easily between people.

Many variants of the coronavirus have cropped up since the pandemic began. But all evidence so far suggests that the new mutant, called B.1.1.7, is more transmissible than previous forms. It first surfaced in September in Britain, but already accounts for more than 60 percent of new cases in London and neighboring areas.

The new variant seems to infect more people than earlier versions of the coronavirus, even when the environments are the same. It’s not clear what gives the variant this advantage, although there are indications that it may infect cells more efficiently.

It’s also difficult to say exactly how much more transmissible the new variant may be, because scientists have not yet done the kind of lab experiments that are required. Most of the conclusions have been drawn from epidemiological observations, and “there’s so many possible biases in all the available data,” cautioned Muge Cevik, an infectious disease expert at the University of St. Andrews in Scotland and a scientific adviser to the British government.

Scientists initially estimated that the new variant was 70 percent more transmissible, but a recent modeling study pegged that number at 56 percent. Once researchers sift through all the data, it’s possible that the variant will turn out to be just 10 to 20 percent more transmissible, said Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle.

Even so, Dr. Bedford said, it is likely to catch on rapidly and become the predominant form in the United States by March. Scientists like Dr. Bedford are tracking all the known variants closely to detect any further changes that might alter their behavior.

Apart from greater transmissibility, the variant behaves like earlier versions.

The new mutant virus may spread more easily, but in every other way it seems little different than its predecessors.

So far, at least, the variant does not seem to make people any sicker or lead to more deaths. Still, there is cause for concern: A variant that is more transmissible will increase the death toll simply because it will spread faster and infect more people.

“In that sense, it’s just a numbers game,” Dr. Rasmussen said. The effect will be amplified “in places like the U.S. and the U.K., where the health care system is really at its breaking point.”

The routes of transmission — by large and small droplets, and tiny aerosolized particles adrift in crowded indoor spaces — have not changed. That means masks, limiting time with others and improving ventilation in indoor spaces will all help contain the variant’s spread, as these measures do with other variants of the virus.

“By minimizing your exposure to any virus, you’re going to reduce your risk of getting infected, and that’s going to reduce transmission over all,” Dr. Rasmussen said.

A drive-through Covid testing site at Dodger Stadium in Los Angeles on Wednesday.
A drive-through Covid testing site at Dodger Stadium in Los Angeles on Wednesday.Credit…Mario Tama/Getty Images

Infection with the new variant may increase the amount of virus in the body.

Some preliminary evidence from Britain suggests that people infected with the new variant tend to carry greater amounts of the virus in their noses and throats than those infected with previous versions.

“We’re talking in the range between 10-fold greater and 10,000-fold greater,” said Michael Kidd, a clinical virologist at Public Health England and a clinical adviser to the British government who has studied the phenomenon.

There are other explanations for the finding — Dr. Kidd and his colleagues did not have access to information about when in their illness people were tested, for example, which could affect their so-called viral loads.

Still, the finding does offer one possible explanation for why the new variant spreads more easily. The more virus that infected people harbor in their noses and throats, the more they expel into the air and onto surfaces when they breathe, talk, sing, cough or sneeze.

As a result, situations that expose people to the virus carry a greater chance of seeding new infections. Some new data indicate that people infected with the new variant spread the virus to more of their contacts.

With previous versions of the virus, contact tracing suggested that about 10 percent of people who have close contact with an infected person — within six feet for at least 15 minutes — inhaled enough virus to become infected.

“With the variant, we might expect 15 percent of those,” Dr. Bedford said. “Currently risky activities become more risky.”

Scientists are still learning how the mutations have changed the virus.

The variant has 23 mutations, compared with the version that erupted in Wuhan, China, a year ago. But 17 of those mutations appeared suddenly, after the virus diverged from its most recent ancestor.

Each infected person is a crucible, offering opportunities for the virus to mutate as it multiplies. With more than 83 million people infected worldwide, the coronavirus is amassing mutations faster than scientists expected at the start of the pandemic.

The vast majority of mutations provide no advantage to the virus and die out. But mutations that improve the virus’ fitness or transmissibility have a greater chance to catch on.

At least one of the 17 new mutations in the variant contributes to its greater contagiousness. The mechanism is not yet known. Some data suggest that the new variant may bind more tightly to a protein on the surface of human cells, allowing it to more readily infect them.

It’s possible that the variant blooms in an infected person’s nose and throat, but not in the lungs, for example — which may explain why patients spread it more easily but do not develop illnesses more severe than those caused by earlier versions of the virus. Some influenza viruses behave similarly, experts noted.

“We need to look at this evidence as preliminary and accumulating,” Dr. Cevik said of the growing data on the new variant.

Still, the research so far suggests an urgent need to cut down on transmission of the variant, she added: “We need to be much more careful over all, and look at the gaps in our mitigation measures.”

Covid-19: How Much Herd Immunity is Enough?

Scientists initially estimated that 60 to 70 percent of the population needed to acquire resistance to the coronavirus to banish it. Now Dr. Anthony Fauci and others are quietly shifting that number upward.

How Much Herd Immunity Is Enough?

How Much Herd Immunity Is Enough?

Scientists initially estimated that 60 to 70 percent of the population needed to acquire resistance to the coronavirus to banish it. Now Dr. Anthony Fauci and others are quietly shifting that number upward.

Dr. Anthony S. Fauci in March. “We really don’t know what the real number is,” he said recently.
Dr. Anthony S. Fauci in March. “We really don’t know what the real number is,” he said recently.Credit…Doug Mills/The New York Times
Donald G. McNeil Jr.

  • Dec. 24, 2020, 5:00 a.m. ET

At what point does a country achieve herd immunity? What portion of the population must acquire resistance to the coronavirus, either through infection or vaccination, in order for the disease to fade away and life to return to normal?

Since the start of the pandemic, the figure that many epidemiologists have offered has been 60 to 70 percent. That range is still cited by the World Health Organization and is often repeated during discussions of the future course of the disease.

Although it is impossible to know with certainty what the limit will be until we reach it and transmission stops, having a good estimate is important: It gives Americans a sense of when we can hope to breathe freely again.

Recently, a figure to whom millions of Americans look for guidance — Dr. Anthony S. Fauci, an adviser to both the Trump administration and the incoming Biden administration — has begun incrementally raising his herd-immunity estimate.

In the pandemic’s early days, Dr. Fauci tended to cite the same 60 to 70 percent estimate that most experts did. About a month ago, he began saying “70, 75 percent” in television interviews. And last week, in an interview with CNBC News, he said “75, 80, 85 percent” and “75 to 80-plus percent.”

In a telephone interview the next day, Dr. Fauci acknowledged that he had slowly but deliberately been moving the goal posts. He is doing so, he said, partly based on new science, and partly on his gut feeling that the country is finally ready to hear what he really thinks.

Hard as it may be to hear, he said, he believes that it may take close to 90 percent immunity to bring the virus to a halt — almost as much as is needed to stop a measles outbreak.

Asked about Dr. Fauci’s conclusions, prominent epidemiologists said that he might be proven right. The early range of 60 to 70 percent was almost undoubtedly too low, they said, and the virus is becoming more transmissible, so it will take greater herd immunity to stop it.

Dr. Fauci said that weeks ago, he had hesitated to publicly raise his estimate because many Americans seemed hesitant about vaccines, which they would need to accept almost universally in order for the country to achieve herd immunity.

Now that some polls are showing that many more Americans are ready, even eager, for vaccines, he said he felt he could deliver the tough message that the return to normal might take longer than anticipated.

“When polls said only about half of all Americans would take a vaccine, I was saying herd immunity would take 70 to 75 percent,” Dr. Fauci said. “Then, when newer surveys said 60 percent or more would take it, I thought, ‘I can nudge this up a bit,’ so I went to 80, 85.

“We need to have some humility here,” he added. “We really don’t know what the real number is. I think the real range is somewhere between 70 to 90 percent. But, I’m not going to say 90 percent.”

Doing so might be discouraging to Americans, he said, because he is not sure there will be enough voluntary acceptance of vaccines to reach that goal. Although sentiments about vaccines in polls have bounced up and down this year, several current ones suggest that about 20 percent of Americans say they are unwilling to accept any vaccine.

Also, Dr. Fauci noted, a herd-immunity figure at 90 percent or above is in the range of the infectiousness of measles.

“I’d bet my house that Covid isn’t as contagious as measles,” he said.

Measles is thought to be the world’s most contagious disease; it can linger in the air for hours or drift through vents to infect people in other rooms. In some studies of outbreaks in crowded military barracks and student dormitories, it has kept transmitting until more than 95 percent of all residents are infected.

Interviews with epidemiologists regarding the degree of herd immunity needed to defeat the coronavirus produced a range of estimates, some of which were in line with Dr. Fauci’s. They also came with a warning: All answers are merely “guesstimates.”

“You tell me what numbers to put in my equations, and I’ll give you the answer,” said Marc Lipsitch, an epidemiologist at Harvard’s T.H. Chan School of Public Health. “But you can’t tell me the numbers, because nobody knows them.”

The only truly accurate measures of herd immunity are done in actual herds and come from studying animal viruses like rinderpest and foot-and-mouth disease, said Dr. David M. Morens, Dr. Fauci’s senior adviser on epidemiology at the National Institute of Allergy and Infectious Diseases.

When cattle are penned in corrals, it is easy to measure how fast a disease spreads from one animal to another, he said. Humans move around, so studying disease spread among them is far harder.

The original assumption that it would take 60 to 70 percent immunity to stop the disease was based on early data from China and Italy, health experts noted.

Epidemiologists watching how fast cases doubled in those outbreaks calculated that the virus’s reproduction number, or R0 — how many new victims each carrier infected — was about 3. So two out of three potential victims would have to become immune before each carrier infected fewer than one. When each carrier infects fewer than one new victim, the outbreak slowly dies out.

Two out of three is 66.7 percent, which established the range of 60 to 70 percent for herd immunity.

The French aircraft carrier Charles de Gaulle arriving in the port of Toulon in April, carrying infected sailors.
The French aircraft carrier Charles de Gaulle arriving in the port of Toulon in April, carrying infected sailors.Credit… Marine Nationale, via Agence France-Presse — Getty Images

Reinforcing that notion was a study conducted by the French military on the crew of the aircraft carrier Charles de Gaulle, which had an outbreak in late March, said Dr. Christopher J.L. Murray, director of the University of Washington’s Institute for Health Metrics and Evaluation.

The study found that 1,064 of the 1,568 sailors aboard, or about 68 percent, had tested positive for the virus.

But the carrier returned to port while the outbreak was still in progress, and the crew went into quarantine, so it was unclear whether the virus was finished infecting new sailors even after 68 percent had caught it.

Also, outbreaks aboard ships are poor models for those on land because infections move much faster in the close quarters of a vessel than in a free-roaming civilian population, said Dr. Natalie E. Dean, a biostatistician at the University of Florida.

More important, the early estimates from Wuhan and Italy were later revised upward, Dr. Lipsitch noted, once Chinese scientists realized they had undercounted the number of victims of the first wave. It took about two months to be certain that there were many asymptomatic people who had also spread the virus.

It also became clearer later that “superspreader events,” in which one person infects dozens or even hundreds of others, played a large role in spreading Covid-19. Such events, in “normal” populations — in which no one wears masks and everyone attends events like parties, basketball tournaments or Broadway shows — can push the reproduction number upward to 4, 5 or even 6, experts said. Consequently, those scenarios call for higher herd immunity; for example, at an R0 of 5, more than four out of five people, or 80 percent, must be immune to slow down the virus.

Further complicating matters, there is a growing consensus among scientists that the virus itself is becoming more transmissible. A variant “Italian strain” with the mutation known as D614G has spread much faster than the original Wuhan variant. A newly identified mutation, sometimes called N501Y, that may make the virus even more infectious has recently appeared in Britain, South Africa and elsewhere.

The more transmissible a pathogen, the more people must become immune in order to stop it.

Dr. Morens and Dr. Lipsitch agreed with Dr. Fauci that the level of herd immunity needed to stop Covid-19 could be 85 percent or higher. “But that’s a guesstimate,” Dr. Lipsitch emphasized.

“Tony’s reading the tea leaves,” Dr. Morens said.

The Centers for Disease Control and Prevention offers no herd immunity estimate, saying on its website that “experts do not know.”

Although W.H.O. scientists still sometimes cite the older 60 to 70 percent estimate, Dr. Katherine O’Brien, the agency’s director of immunization, said that she now thought that range was too low. She declined to estimate what the correct higher one might be.

“We’d be leaning against very thin reeds if we tried to say what level of vaccine coverage would be needed to achieve it,” she said. “We should say we just don’t know. And it won’t be a world or even national number. It will depend on what community you live in.”

Dr. Dean noted that to stop transmission in a crowded city like New York, more people would have to achieve immunity than would be necessary in a less crowded place like Montana.

Even if Dr. Fauci is right and it will take 85 or even 90 percent herd immunity to completely stop coronavirus transmission, Dr. Lipsitch said, “we can still defang the virus sooner than that.”

He added: “We don’t have to have zero transmission in order to have a decent society. We have lots of diseases, like flu, transmitting all the time, and we don’t shut down society for that. If we can vaccinate almost all the people who are most at risk of severe outcomes, then this would become a milder disease.”

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