Tagged SARS (Severe Acute Respiratory Syndrome)

Studies Suggest People Who Had Covid-19 Should Get Single Vaccine Dose

People Who Have Had Covid Should Get Single Vaccine Dose, Studies Suggest

New studies show that one shot of a vaccine can greatly amplify antibody levels in those who have recovered from the coronavirus.

A nurse supervisor prepared a dose of the Pfizer-BioNTech vaccine at a mass vaccination site in Hartford, Conn., this month.
A nurse supervisor prepared a dose of the Pfizer-BioNTech vaccine at a mass vaccination site in Hartford, Conn., this month.Credit…Christopher Capozziello for The New York Times
Apoorva Mandavilli

  • Feb. 19, 2021Updated 11:49 a.m. ET

Nearly 30 million people in the United States — and probably many others whose illnesses were never diagnosed — have been infected with the coronavirus so far. Should these people still be vaccinated?

Two new studies answer that question with an emphatic yes.

In fact, the research suggests that for these people just one dose of the vaccine is enough to turbocharge their antibodies and destroy the coronavirus — and even some more infectious variants.

The results of these new studies are consistent with the findings of two others published over the past few weeks. Taken together, the research suggests that people who have had Covid-19 should be immunized — but a single dose of the vaccine may be enough.

“I think it’s a really strong rationale for why people who were previously infected with Covid should be getting the vaccine,” said Jennifer Gommerman, an immunologist at the University of Toronto who was not involved in the new research.

A person’s immune response to a natural infection is highly variable. Most people make copious amounts of antibodies that persist for many months. But some people who had mild symptoms or no symptoms of Covid-19 produce few antibodies, which quickly fall to undetectable levels.

The vaccines “even the playing field,” Dr. Gommerman said, so that anyone who has recovered from Covid-19 produces enough antibodies to protect against the virus.

The latest study, which has not yet been published in a scientific journal, analyzed blood samples from people who have had Covid-19. The findings suggested that their immune systems would have trouble fending off B.1.351, the coronavirus variant first identified in South Africa.

But one shot of either the Pfizer-BioNTech or Moderna vaccine significantly changed the picture: It amplified the amount of antibodies in their blood by a thousandfold — “a massive, massive boost,” said Andrew T. McGuire, an immunologist at the Fred Hutchinson Cancer Research Center in Seattle, who led the study.

Flush with antibodies, samples from all of the participants could neutralize not only B.1.351, but also the coronavirus that caused the SARS epidemic in 2003.

In fact, the antibodies seemed to perform better than those in people who had not had Covid and had received two doses of a vaccine. Multiple studies have suggested that the Pfizer-BioNTech and Moderna vaccines are about five times less effective against the variant.

A Covid-19 patient in the intensive care unit of Marian Regional Medical Center in Santa Maria, Calif., this month.
A Covid-19 patient in the intensive care unit of Marian Regional Medical Center in Santa Maria, Calif., this month.Credit…Daniel Dreifuss for The New York Times

The researchers obtained blood samples from 10 volunteers in the Seattle Covid Cohort Study who were vaccinated months after contracting the coronavirus. Seven of the participants received the Pfizer-BioNTech vaccine and three received the Moderna vaccine.

Blood taken about two to three weeks after vaccination showed a significant jump in the amounts of antibodies compared with the samples collected before vaccination. The researchers don’t yet know how long the increased amount of antibodies will persist, but “hopefully, they’ll last a long time,” Dr. McGuire said.

The researchers also saw increases in immune cells that remember and fight the virus, Dr. McGuire said. “It looks pretty clear that we’re boosting their pre-existing immunity,” he said.

In another new study, researchers at New York University found that a second dose of the vaccine did not add much benefit at all for people who have had Covid-19 — a phenomenon that has also been observed with vaccines for other viruses.

In that study, most people had been infected with the coronavirus eight or nine months earlier, but saw their antibodies increase by a hundredfold to a thousandfold when given the first dose of a vaccine. After the second dose, however, the antibody levels did not increase any further.

“It’s a real testament to the strength of the immunologic memory that they get a single dose and have a huge increase,” said Dr. Mark J. Mulligan, director of the N.Y.U. Langone Vaccine Center and the study’s lead author.

In some parts of the world, including the United States, a significant minority of the population has already been infected, Dr. Mulligan noted. “They definitely should be vaccinated,” he said.

It’s unclear whether the thousandfold spike in antibody levels recorded in the lab will occur in real-life settings. Still, the research shows that a single shot is enough to increase the levels of antibodies significantly, said Florian Krammer, an immunologist at the Icahn School of Medicine at Mount Sinai in New York.

Dr. Krammer led another of the new studies, which showed that people who have had Covid-19 and received one dose of a vaccine experienced more severe side effects from the inoculation and had more antibodies compared with those who had not been infected before.

“If you put all four papers together, that’s providing pretty good information about people who already had an infection only needing one vaccination,” Dr. Krammer said.

He and other researchers are trying to persuade scientists at the Centers for Disease Control and Prevention to recommend only one dose for those who have recovered from Covid-19.

A woman receives a vaccine at a drive-through site in Hartford.Credit…Christopher Capozziello for The New York Times

Ideally, those people should be monitored after the first shot in case their antibody levels plummet after some weeks or months, said Dennis R. Burton, an immunologist at the Scripps Research Institute in La Jolla, Calif.

The fact that the supercharged antibodies observed in the new study can fight the 2003 SARS virus suggests that a single dose of the vaccine may have prompted the volunteers’ bodies to produce “broadly neutralizing antibodies” — immune molecules capable of attacking a broad range of related viruses, Dr. Burton said.

He and other scientists have for decades investigated whether broadly neutralizing antibodies can tackle multiple versions of H.I.V. at once. H.I.V. mutates faster than any other virus and quickly evades most antibodies.

The new coronavirus mutates much more slowly, but there are now multiple variants of the virus that seem to have evolved to be more contagious or to thwart the immune system. The new study may provide clues on how to make a single vaccine that stimulates the production of broadly neutralizing antibodies that can destroy all variants of the coronavirus, Dr. Burton said.

Without such a vaccine, scientists will need to tweak the vaccines every time the virus changes significantly. “You’re stuck in a kind of Whac-a-Mole approach,” he said. It will probably take many months if not longer to develop and test that sort of vaccine against the coronavirus, but “that’s the longer-term way to approach this virus.”

People Who Have Had Covid Should Get Single Vaccine Dose, Studies Suggest

People Who Have Had Covid Should Get Single Vaccine Dose, Studies Suggest

New studies show that one shot of a vaccine can greatly amplify antibody levels in those who have recovered from the coronavirus.

A nurse supervisor prepared a dose of the Pfizer-BioNTech vaccine at a mass vaccination site in Hartford, Conn., this month.
A nurse supervisor prepared a dose of the Pfizer-BioNTech vaccine at a mass vaccination site in Hartford, Conn., this month.Credit…Christopher Capozziello for The New York Times
Apoorva Mandavilli

  • Feb. 19, 2021, 9:49 a.m. ET

At least 30 million people in the United States — and probably many others whose illnesses were never diagnosed — have been infected with the coronavirus so far. Should these people still be vaccinated?

Two new studies answer that question with an emphatic yes.

In fact, the research suggests that for these people just one dose of the vaccine is enough to turbocharge their antibodies and destroy the coronavirus — and even some more infectious variants.

The results of these new studies are consistent with the findings of two others published over the past few weeks. Taken together, the research suggests that people who have had Covid-19 should be immunized — but a single dose of the vaccine may be enough.

“I think it’s a really strong rationale for why people who were previously infected with Covid should be getting the vaccine,” said Jennifer Gommerman, an immunologist at the University of Toronto who was not involved in the new research.

A person’s immune response to a natural infection is highly variable. Most people make copious amounts of antibodies that persist for many months. But some people who had mild symptoms or no symptoms of Covid-19 produce few antibodies, which quickly fall to undetectable levels.

The vaccines “even the playing field,” Dr. Gommerman said, so that anyone who has recovered from Covid-19 produces enough antibodies to protect against the virus.

The latest study, which has not yet been published in a scientific journal, analyzed blood samples from people who have had Covid-19. The findings suggested that their immune systems would have trouble fending off B.1.351, the coronavirus variant first identified in South Africa.

But one shot of either the Pfizer-BioNTech or Moderna vaccine significantly changed the picture: It amplified the amount of antibodies in their blood by a thousandfold — “a massive, massive boost,” said Andrew T. McGuire, an immunologist at the Fred Hutchinson Cancer Research Center in Seattle, who led the study.

Flush with antibodies, samples from all of the participants could neutralize not only B.1.351, but also the coronavirus that caused the SARS epidemic in 2003.

In fact, the antibodies seemed to perform better than those in people who had not had Covid and had received two doses of a vaccine. Multiple studies have suggested that the Pfizer-BioNTech and Moderna vaccines are about five times less effective against the variant.

A Covid-19 patient in the intensive care unit of Marian Regional Medical Center in Santa Maria, Calif., this month.
A Covid-19 patient in the intensive care unit of Marian Regional Medical Center in Santa Maria, Calif., this month.Credit…Daniel Dreifuss for The New York Times

The researchers obtained blood samples from 10 volunteers in the Seattle Covid Cohort Study who were vaccinated months after contracting the coronavirus. Seven of the participants received the Pfizer-BioNTech vaccine and three received the Moderna vaccine.

Blood taken about two to three weeks after vaccination showed a significant jump in the amounts of antibodies compared with the samples collected before vaccination. The researchers don’t yet know how long the increased amount of antibodies will persist, but “hopefully, they’ll last a long time,” Dr. McGuire said.

The researchers also saw increases in immune cells that remember and fight the virus, Dr. McGuire said. “It looks pretty clear that we’re boosting their pre-existing immunity,” he said.

In another new study, researchers at New York University found that a second dose of the vaccine did not add much benefit at all for people who have had Covid-19 — a phenomenon that has also been observed with vaccines for other viruses.

In that study, most people had been infected with the coronavirus eight or nine months earlier, but saw their antibodies increase by a hundredfold to a thousandfold when given the first dose of a vaccine. After the second dose, however, the antibody levels did not increase any further.

“It’s a real testament to the strength of the immunologic memory that they get a single dose and have a huge increase,” said Dr. Mark J. Mulligan, director of the N.Y.U. Langone Vaccine Center and the study’s lead author.

In some parts of the world, including the United States, a significant minority of the population has already been infected, Dr. Mulligan noted. “They definitely should be vaccinated,” he said.

It’s unclear whether the thousandfold spike in antibody levels recorded in the lab will occur in real-life settings. Still, the research shows that a single shot is enough to increase the levels of antibodies significantly, said Florian Krammer, an immunologist at the Icahn School of Medicine at Mount Sinai in New York.

Dr. Krammer led another of the new studies, which showed that people who have had Covid-19 and received one dose of a vaccine experienced more severe side effects from the inoculation and had more antibodies compared with those who had not been infected before.

“If you put all four papers together, that’s providing pretty good information about people who already had an infection only needing one vaccination,” Dr. Krammer said.

He and other researchers are trying to persuade scientists at the Centers for Disease Control and Prevention to recommend only one dose for those who have recovered from Covid-19.

A woman receives a vaccine at a drive-through site in Hartford.Credit…Christopher Capozziello for The New York Times

Ideally, those people should be monitored after the first shot in case their antibody levels plummet after some weeks or months, said Dennis R. Burton, an immunologist at the Scripps Research Institute in La Jolla, Calif.

The fact that the supercharged antibodies observed in the new study can fight the 2003 SARS virus suggests that a single dose of the vaccine may have prompted the volunteers’ bodies to produce “broadly neutralizing antibodies” — immune molecules capable of attacking a broad range of related viruses, Dr. Burton said.

He and other scientists have for decades investigated whether broadly neutralizing antibodies can tackle multiple versions of H.I.V. at once. H.I.V. mutates faster than any other virus and quickly evades most antibodies.

The new coronavirus mutates much more slowly, but there are now multiple variants of the virus that seem to have evolved to be more contagious or to thwart the immune system. The new study may provide clues on how to make a single vaccine that stimulates the production of broadly neutralizing antibodies that can destroy all variants of the coronavirus, Dr. Burton said.

Without such a vaccine, scientists will need to tweak the vaccines every time the virus changes significantly. “You’re stuck in a kind of Whac-a-Mole approach,” he said. It will probably take many months if not longer to develop and test that sort of vaccine against the coronavirus, but “that’s the longer-term way to approach this virus.”

Could a Single Vaccine Work Against All Coronaviruses?

Could a Single Vaccine Work Against All Coronaviruses?

Scientists are working on a shot that could protect against Covid-19, its variants, certain seasonal colds — and the next coronavirus pandemic.

Tara Gallion, a licensed practical nurse, prepared to administer doses of the Moderna Covid vaccine in Mound Bayou, Miss., last month.
Tara Gallion, a licensed practical nurse, prepared to administer doses of the Moderna Covid vaccine in Mound Bayou, Miss., last month.Credit…Rory Doyle for The New York Times
Carl Zimmer

  • Feb. 9, 2021, 11:26 a.m. ET

The invention of Covid-19 vaccines will be remembered as a milestone in the history of medicine, creating in a matter of months what had before taken up to a decade. But Dr. Kayvon Modjarrad, the director of Emerging Infectious Diseases Branch at Walter Reed Army Institute of Research in Silver Springs, Md., isn’t satisfied.

“That’s not fast enough,” he said. More than 2.3 million people around the world have died, and many countries will not have full access to the vaccines for another year or two: “Fast — truly fast — is having it there on day one.”

There will be more coronavirus outbreaks in the future. Bats and other mammals are rife with strains and species of this abundant family of viruses. Some of these pathogens will inevitably spill over the species barrier and cause new pandemics. It’s only a matter of time.

Dr. Modjarrad is one of many scientists who for years have been calling for a different kind of vaccine: one that could work against all coronaviruses. Those calls went largely ignored until Covid-19 demonstrated just how disastrous coronaviruses can be.

Now researchers are starting to develop prototypes of a so-called pancoronavirus vaccine, with some promising, if early, results from experiments on animals. Dr. Eric Topol, a professor of molecular medicine at the Scripps Research Institute in San Diego, thinks scientists should join together in another large-scale vaccine-creation project immediately.

“We have to get a real work force to accelerate this, so we can have it this year,” he said. Dr. Topol and Dennis Burton, a Scripps immunologist, called for this project on broad coronavirus vaccines on Monday in the journal Nature.

After coronaviruses were first identified in the 1960s, they did not become a high priority for vaccine makers. For decades it seemed as if they only caused mild colds. But in 2002, a new coronavirus called SARS-CoV emerged, causing a deadly pneumonia called severe acute respiratory syndrome, or SARS. Scientists scrambled to make a vaccine for it.

Dr. Kayvon Modjarrad, director of emerging infectious diseases at the Walter Reed Army Institute, during a coronavirus briefing in March.
Dr. Kayvon Modjarrad, director of emerging infectious diseases at the Walter Reed Army Institute, during a coronavirus briefing in March.Credit…Yasin Ozturk/Anadolu Agency, via Getty Images

Since no one had made a coronavirus vaccine for humans before, there was a huge amount to learn about its biology. Eventually, researchers chose a target for immunity: a protein on the surface of the virus, called spike. Antibodies that stick to the spike can prevent the coronavirus from entering cells and stop an infection.

Public health officials in Asia and elsewhere did not wait for the invention of a SARS vaccine to get to work, however. Their quarantines and other efforts proved remarkably effective. In a matter of months, they wiped out SARS-CoV, with only 774 deaths along the way.

The danger of coronaviruses became even clearer in 2012, when a second species spilled over from bats, causing yet another deadly respiratory disease called MERS. Researchers started work on MERS vaccines. But some researchers wondered if making a new vaccine for each new coronavirus — what Dr. Modjarrad calls “the one bug, one drug approach” — was the smartest strategy. Wouldn’t it be better, they thought, if a single vaccine could work against SARS, MERS and any other coronavirus?

That idea went nowhere for years. MERS and SARS caused relatively few deaths, and were soon eclipsed by outbreaks of other viruses such as Ebola and Zika.

In 2016, Maria Elena Bottazzi, a virologist at Baylor College of Medicine, and her colleagues applied for support from the American government to develop a pancoronavirus vaccine, but did not receive it. “They said there’s no interest in pancorona,” Dr. Bottazzi recalled.

Her team even lost funding for developing a SARS vaccine after they showed that it worked in mice, was not toxic to human cells and could be manufactured at scale. A coronavirus that had disappeared from view simply wasn’t a top priority.

Without enough money to start clinical trials, the scientists stored their SARS vaccine in a freezer and moved on to other research. “It’s been a struggle,” Dr. Bottazzi said.

Dr. Matthew Memoli, a virologist at the National Institute of Allergy and Infectious Diseases, looks back at those decisions as an enormous blunder. “It’s a failure of our system of science,” he said. “Funders tend to chase after shiny objects.”

A transmission electron micrograph of the Middle East Respiratory Syndrome.Credit…NIAID

Three years later, a third dangerous coronavirus emerged: the SARS-CoV-2 strain that causes Covid-19. Although this virus has a much lower fatality rate than its cousins that cause SARS and MERS, it does a far better job of spreading from person to person, resulting in more than 106 million documented cases around the world and still climbing.

All the lessons that researchers had learned about coronaviruses helped them move quickly to make new vaccines for SARS-CoV-2. Dr. Bottazzi and her colleagues used the technology they had created to make SARS vaccines to make one for Covid-19, which is now in early clinical trials.

Other researchers used even newer methods to move faster. The German company BioNTech created a genetic molecule called messenger RNA that encoded the spike protein. Partnering with Pfizer, the companies received U.S. government authorization for their vaccine in just 11 months. The previous record for a vaccine, against chickenpox, was four years.

Although the Covid-19 pandemic is still far from over, a number of researchers are calling for preparations for the next deadly coronavirus.

“This has already happened three times,” said Daniel Hoft, a virologist at Saint Louis University. “It’s very likely going to happen again.”

Researchers at VBI vaccines, a Cambridge-based company, took a small step toward a pancoronavirus vaccine last summer. They created virus-like shells studded with spike proteins from the three coronaviruses that caused SARS, MERS and Covid-19.

When the researchers injected this three-spike vaccine into mice, the animals made antibodies that worked against all three coronaviruses. Intriguingly, some of those antibodies could also latch onto a fourth human coronavirus that causes seasonal colds — even though that virus’s spike proteins were not included in the vaccine. The scientists have made this data public but have not yet published it in a scientific journal.

David Anderson, VBI’s chief scientific officer, said it was not clear why the vaccine worked this way. One possibility is that an immune cell presented with several versions of a protein at once doesn’t make antibodies against just one. Instead, it makes a compromise antibody that works against them all.

“You’re educating it,” Dr. Anderson said, although he cautioned that this was speculation for now.

Last month, Pamela Bjorkman, a structural biologist at Caltech, and her colleagues published a more extensive experiment with a universal coronavirus vaccine in the journal Science. The researchers attached only the tips of spike proteins from eight different coronaviruses to a protein core, known as a nanoparticle. After injecting these nanoparticles into mice, the animals generated antibodies that could stick to all eight of the coronaviruses — and to four other coronaviruses that the scientists had not used in the vaccine.

Sarah Clarke, a lab technician at the Sequencing and Genomic Technologies Shared Resource at Duke University, working with positive coronavirus samples.Credit…Pete Kiehart for The New York Times

Dr. Modjarrad is leading a team at Walter Reed developing another vaccine based on a nanoparticle studded with protein fragments. They anticipate starting clinical trials on volunteers next month. Although the vaccine currently uses protein fragments only from SARS-CoV-2 spikes, Dr. Modjarrad and his colleagues are preparing to retool it as a pancoronavirus vaccine.

Dr. Hoft of Saint Louis University is working on a universal vaccine that does not rely on antibodies to the spike protein. Collaborating with Gritstone Oncology, a California-based biotech company, he has created a vaccine that prompts cells to make surface proteins that might alert the immune system as if a coronavirus — any coronavirus — were present. They are now preparing a clinical trial to see if it is effective against SARS-CoV-2.

“We are interested to develop maybe a third-generation vaccine, which would be on the shelf and ready for the future outbreak,” Dr. Hoft said.

Dr. Topol believes scientists should also explore another strategy: searching for pancoronavirus antibodies made by our own bodies during infections.

Researchers studying H.I.V. and other viruses have discovered, amid the billions of antibodies made during an infection, rare types that work against a huge range of related strains. It might be possible to create vaccines that coax the body to make abundant amounts of these broadly neutralizing antibodies.

Coronaviruses are similar enough to each other, Dr. Topol said, that it might not be that hard to build vaccines that make broadly neutralizing antibodies. “This is an easy family of viruses to take down,” he said.

The search for a pancoronavirus vaccine may take longer than Dr. Topol’s sunny expectations. But even if it takes a few years, it could help prepare the world for the next coronavirus that jumps the species barrier.

“I think we can have vaccines to prevent pandemics like this,” Dr. Memoli said. “None of us wants to go through this again. And we don’t want our children to go through this again, or our grandchildren, or our descendants 100 years from now.”

Should Isolation Periods Be Shorter for People With Covid-19?

People with Covid-19, the illness caused by the coronavirus, are most infectious about two days before symptoms begin and for five days afterward, according to a new analysis of previous research.

A few patients who are extremely ill or have impaired immune systems may expel — or “shed” — the virus for as long as 20 days, other studies have suggested. Even in mild cases, some patients may shed live virus for about a week, the new analysis found.

The accumulating data presents a quandary: Should public health officials shorten the recommended isolation time if it means more infected people will cooperate? Or should officials opt for longer periods in order to prevent transmission in virtually all cases, even if doing so takes a harsher toll on the economy?

The Centers for Disease Control and Prevention recommends that infected people isolate for a minimum of 10 days from the beginning of their illness. The agency is considering shortening the recommended isolation period and may issue new guidelines as early as next week, according to two federal officials with knowledge of the discussions.

In September, France dropped its required period of isolation to seven days from 14 days, and Germany is considering shortening it to five days. (Isolation refers to people who are ill; quarantine refers to people who have been exposed to the virus and may become ill.)

Setting the isolation period at five days is likely to be much more palatable and may encourage more infected people to comply, said Dr. Muge Cevik, an infectious disease expert at the University of St Andrews in Scotland who led the new analysis, published in the journal The Lancet Microbe.

A recent survey in the United Kingdom showed that only one in five people were able to isolate for 10 days after developing symptoms. “Even if we do more testing, if we can’t ensure people self-isolate, I don’t think we’ll be able to control the spread,” Dr. Cevik said.

In the United States, many people don’t get tested for the infection until a day or two after they begin to feel ill. With the current delays, many receive results two or three days later, toward the end of the period during which they are infectious.

“Even if you were to get the P.C.R. test right on the very first day that you could, by the time you get the results back, 90 percent of your shedding has been completed,” said Dr. Michael Mina, a virologist at the Harvard T.H. Chan School of Public Health. “This meta-analysis shows just how short your transmission window is.”

Dr. Cevik and her colleagues set out to analyze the so-called kinetics of the coronavirus over the course of an infection, and to compare the pathogen to the closely related SARS and MERS viruses.

The researchers considered nearly 1,500 studies published from 2003 to June 2020 on the timing of infection in thousands of people, most of whom were sick enough to be hospitalized. The team drew data from 79 studies of the new coronavirus, 11 studies of MERS and eight studies of SARS.

People who never develop symptoms seem to carry about the same amount of the new coronavirus as symptomatic patients, Dr. Cevik and her colleagues found. But asymptomatic people seem to clear the virus more quickly from their bodies.

People with Covid-19 usually are most infectious a day or two before the onset of symptoms until about five days after, the analysis concluded. Yet patients may carry genetic fragments from the virus in their noses and throats for an average of 17 days, and, in some cases, for up to three months.

A few patients may carry infectious virus in their lungs — as opposed to the nose and throat — for as long as eight days after symptoms begin, noted Dr. Megan Ranney, an emergency physician at Brown University. For these patients, at least, isolation periods should probably be longer than five days, if only they could be identified.

“The trouble is, who has Covid pneumonia versus who doesn’t is not always fully apparent just based on physical exam,” she said. “They wouldn’t know it on their own.”

Older people tend to be infectious for longer than younger people, but no study in the analysis detected live virus beyond nine days of symptom onset. The results suggest that positive tests after that point find only genetic fragments, rather than whole live virus, Dr. Cevik said.

Because the infectious period seems to peak relatively quickly in the course of the illness, health care workers at community clinics may be at higher risk of becoming infected than those working in I.C.U. units, where patients tend to be in the later stages, Dr. Cevik added.

The analysis underscores data that have accumulated since March. In July, based on similar evidence, the C.D.C. truncated its recommendation for isolation to 10 days from 14 days.

But even at 10 days, the isolation period may be too long for many people, experts said. Patients may be financially unable to isolate for so long, or they may not feel sick enough to want to do so.

“If you could make that shorter for people, I think that would really help people comply with the public health guidelines,” said Angela Rasmussen, a virologist affiliated with the Center for Global Health Science and Security at Georgetown University, referring to the recommended isolation period.

But the new analysis is limited by the fact that only a few of the included studies looked at live virus, she added.

Some people who are older or very sick may be infectious for longer than a week. But if a shorter recommended period encourages more people to isolate, the benefit will more than offset any risk to the community from the small amount of virus that a few patients may still carry after five days, said Dr. Stefan Baral, an epidemiologist at Johns Hopkins University.

But some doctors said that they were not convinced by the analysis that five days of isolation would prevent transmission from a majority of people.

“There’s a sweet spot there, I would imagine, but I haven’t figured out where that is,” said Dr. Taison Bell, a critical care and infectious disease physician at the University of Virginia.

Dr. Cevik and other experts suggest that people can isolate as soon as they experience even mild symptoms, such as a sore throat or head and body aches — without venturing out for a P.C.R. test right when they are most infectious.

But Dr. Bell said he was unsure how this would work in practice, because these early symptoms were similar to those from other viral infections, including the common cold.

Dr. Cevik said a P.C.R. test should be performed after isolation ended, to confirm the diagnosis. Alternately, it may make sense to take a rapid antigen test — which can detect high amounts of virus — while isolating, to confirm an active coronavirus infection.

Other experts also endorsed the use of at-home rapid tests. “I think that’s a lovely solution,” Dr. Ranney said. “If you have symptoms, and you have a reliable test that you can do at home, stay home, test at home and isolate for five days.”

Over all, the new analysis underscores how quickly the coronavirus blooms in the body and the speed with which both patients and doctors must respond to keep it contained, Dr. Baral said. Levels of the MERS virus peak at seven to 10 days from symptom onset, and those of the SARS virus peak at Days 10 to 14.

By contrast, the new coronavirus “moves quick,” Dr. Baral said. “It’s a very difficult virus to control, as compared to SARS.”

Home isolation is safe for most of those newly infected with the coronavirus, he added — essentially the model of care that doctors use for patients suspected of having influenza.

Some countries already have adopted policies to make it easier for people to isolate. Vietnam provides income support to people who need to take time off work. Until May, the Japanese government asked patients who were young and had mild symptoms to stay home for four days before seeking testing.

Japan’s guidelines now ask patients to consult by phone with their doctors and to seek testing only if they seem likely to be infected. Anyone who tests positive is admitted to a hospital or a hotel to isolate. In the United States, New York City and Vermont have made similar accommodations available to infected patients.

Even if the rest of the country doesn’t implement such policies, having patients isolate at home — while wearing a mask, keeping windows open, cleaning high-touch surfaces and staying far from other household members — is more feasible for five days than for 10, Dr. Baral said.

“I do think there’s an element of diminishing returns with those last four or five days,” he said. “An intense amount of isolation during that first five to seven days would avert a ton of infections — a ton.”

Makiko Inoue contributed reporting from Tokyo.