The Food and Drug Administration authorized a third dose of the Pfizer-BioNTech Covid-19 vaccine Wednesday for emergency use in people ages 65 and up, as well as those 18 and older at high risk of exposure to the coronavirus or severe illness. Boosters are to be given at least six months after people get their second doses of the Pfizer vaccine.
An advisory group to the Centers for Disease Control and Prevention opened a two-day meeting on the safety and effectiveness of Pfizer's booster shot. The advisers will vote Thursday on who would qualify for third shots.
Recommendation from the CDC group, called the Advisory Committee on Immunization Practices, or ACIP, is needed before booster shots can be administered. If the head of the CDC, Dr. Rochelle Walensky, signs off on the committee's recommendation, third doses of the Pfizer vaccine could be administered promptly.
The timing of the FDA authorization cast an air of uncertainty over the first day of the meeting of the ACIP, whose members usually know at the outset what FDA decision it will be considering. Instead, the FDA announcement did not come until after the meeting concluded for the day Wednesday.
Pfizer originally asked the FDA to consider third doses for everyone 16 and older six months after they received their second doses. An FDA advisory committee rejected the request Friday, limiting the booster to older adults and those most likely to become seriously ill from Covid-19.
The advisory committee also suggested that people at high risk of exposure at work, such as health care workers and teachers, should be eligible for booster doses.
That was reflected in Wednesday's emergency use authorization. "Health care workers, teachers and day care staff, grocery workers and those in homeless shelters or prisons, among others," will be able to get third doses of the Pfizer vaccine, the acting FDA commissioner, Dr. Janet Woodcock, said in a statement.
Additional data on the safety and effectiveness of boosters are expected in the coming weeks. "We will continue to evaluate the rapidly changing science and keep the public informed," Woodcock said.
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The booster dose is aimed at combating waning immunity from the original series of the vaccine. Data from Israel, presented at Friday's advisory committee meeting, suggest that protection from Pfizer's vaccine drops off significantly after six months, although data from the U.S. show less of a decline, particularly against severe disease. Early data from Israel also showed that booster doses offered more protection against infection.
In rejecting Pfizer's original request — that boosters be made available to everyone 16 and older — the FDA committee cited concerns about the shot's possible side effects in younger adults, such as myocarditis.
ACIP members also struck a skeptical tone for much of Wednesday’s discussions. In addition to requests for more data, committee members wanted more clarity about the specific goal of booster doses: Is it to prevent all illness or just severe disease?
Another thorny question the CDC advisers will continue to discuss Thursday is what people who were originally vaccinated with Moderna or Johnson & Johnson should do, as Wednesday's emergency use authorization included only people who received Pfizer's vaccine.
"That's going to leave half of people immunized being told that they’re at risk now of waning immunity and hospitalization and unable to get a booster dose," said ACIP member, Dr. Sarah Long, a professor of pediatrics at Drexel University College of Medicine in Philadelphia. "That’s a big public health panic that we would like to avoid.”
Moderna has submitted data about its booster dose to the FDA, and Johnson & Johnson is working on doing the same.