Flu Vaccine in Pregnancy Offers Brief Protection of Babies

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Unborn babies are temporarily protected by their mother’s flu shot, but that immunity fades within weeks after birth, a new study found.

In a randomized, double-blind placebo-controlled study, researchers measured the efficacy of the flu vaccine on the unborn children of vaccinated pregnant women by comparing rates of disease and levels of antibodies in 1,026 infants born to vaccinated women and 1,023 controls born to unvaccinated mothers. The study, which was paid for by the Gates Foundation, is online in JAMA Pediatrics.

The vaccine was about 86 percent effective until the babies were 8 weeks old. But between 8 and 24 weeks, its power dropped rapidly, and the effect of the vaccine became statistically insignificant.

The lead author, Marta C. Nunes, a researcher at the University of Witwatersrand in Johannesburg, stressed that vaccination during pregnancy is nevertheless essential.

“It’s still important to vaccinate women during pregnancy,” she said. “Pregnant women are a high-risk group, and vaccinating them protects them as well as their babies.”

Finding a vaccine for pregnant women that confers long-lasting immunity on the baby is important because no flu vaccine is approved for babies under the age of 6 months.

“We have to work on creating vaccines that work in babies or that are more immunogenic in the mother so that her antibodies last longer,” she said.