A U.S. Food and Drug Administration (FDA) committee voted unanimously Friday to recommend booster doses of Pfizer-BioNTech’s COVID-19 vaccine for those over age 65 and those at higher risk of exposure to the virus, including healthcare, frontline and essential workers, under emergency use authorization, but stopped short of recommending boosters for the general population. (Boosters have already been authorized for those with compromised immune systems.)
Pfizer-BioNTech had originally requested that the FDA consider full approval of a booster dose for all people who have been vaccinated with its shot. The 18 members of the committee voted initially 16 to 2 against that move, citing the lack of strong enough data on safety and effectiveness of boosting the general population at this time. The FDA then reworded Pfizer-BioNTech’s original request to include only those at highest risk of COVID-19, which earned a unanimous vote in favor.
The FDA’s acting commissioner, Janet Woodcock, will take the committee’s recommendation into consideration before making a final decision. If the FDA follows the advice, then the U.S. Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices (ACIP) will review the data and make a recommendation to doctors and health care workers about how the booster will be administered. One important question the ACIP must address, for example, is whether Pfizer-BioNTech’s booster dose should be limited to those who have already received two doses of the companies’ vaccine, since the data reviewed by the FDA committee only included a small subset of those recipients and not people who received the other authorized shots from Moderna and Johnson & Johnson-Janssen.
The committee advised that most of the U.S. population will have to wait to get a booster dose, guidance that directly contradicts the recommendation by U.S. President Joe Biden’s health team, which planned to start widely rolling out boosters on September 20, pending FDA authorization or approval.
The decision heightens the growing tension over the booster question, as public health officials, infectious disease specialists and policy makers disagree about exactly how useful another dose of COVID-19 vaccine can be. The FDA committee members noted that while there is evidence that vaccine-induced immunity wanes over time, giving fully vaccinated people another dose of vaccine will likely have little impact on actually controlling the pandemic in the U.S., since most new cases and severe illnesses are driven by the unvaccinated.
Over Friday’s day-long meeting, the committee members debated the strength and quality of data showing waning protection among everyone who has been vaccinated so far, and what it means for controlling transmission and spread of COVID-19. The panel members heard from Israeli public health officials, who have the most in depth, although still incomplete, data on waning immunity and the impact of a booster dose, as well as U.S. CDC researchers who understand the dynamics of the U.S. pandemic.
In making its case for a booster, Pfizer-BioNTech acknowledged that about a month after the second of the two doses in the regimen, its vaccine is 96% efficacious in protecting people from symptoms of COVID-19. About two to four months later, that efficacy slips to 90%, and by six months, it drops to 84%—about a 6% decline every two months. And while Pfizer-BioNTech provided data showing an additional dose of its vaccine could increase levels of neutralizing antibodies against SARS-CoV-2, the virus that causes COVID-19, it did not provide answers to questions about how well that protection could stop transmission of the disease, among other things, to the committee’s satisfaction.
Pfizer-BioNTech maintains that protection from its vaccine remains high enough to shield people from severe illness and in most cases, hospitalization and death; most vaccinated people who get infected experience mild disease. But there are worrying signs that with the Delta variant, the more transmissible variant that is now the dominant virus behind new infections, even that trend is changing.
In its latest analyses provided to the FDA, however, the company said that even though levels of antibodies didn’t jump after the first dose, people were still protected against COVID-19 disease; when they compared disease symptoms among people who received only one dose and those who remained unvaccinated, the partially vaccinated enjoyed fewer symptoms after about a week. It turns out that immunity continues to build with each successive dose. Their data also showed that boosting this protection again can be done with another dose of the existing vaccine, even if Delta is causing more infections. The increased levels of antibodies generated by this dose were high enough to neutralize even Delta, as well as other variants including Beta and Gamma.
From a public health point of view, however, those concerns may seem semantic, and the committee’s recommendation will likely continue to divide experts in the field. While it’s true that the current two-dose vaccine does protect well against severe disease, any COVID-19 disease continues to strain the already struggling health care system. And any disease, especially with Delta, which transmits far more easily among people than earlier variants of the virus, could be dangerous to public health.
“It’s not just about serious illness and death, but about people getting infected and spreading the virus,” says Dr. Otto Yang, professor of medicine and infectious disease at University of California Los Angeles, who is not part of the FDA advisory committee. “If people can get breakthrough infections, even if they don’t get sick they can spread the virus. And that’s a problem for society, especially when a large percentage of people are not vaccinated. And even mild infection can cause significant health problems in people, from clotting to heart attacks, strokes, and long COVID. So not getting infected is clearly a benefit.”
The committee members noted that because the recommendation is under Emergency Use Authorization (EUA), it could be revised as more data come in to support the need to broaden the groups eligible for a booster dose. For now, they say, the focus should be on continuing to reach people who haven’t been vaccinated at all; that will likely have the biggest impact on slowing the spread of the virus and ultimately getting the COVID-19 pandemic under control.
Dr. Arnold Monto, who chairs the FDA advisory panel, applauded the agency’s willingness to withhold a full-throated call for boosters until a stronger case can be made. And he suggested that as more evidence accumulates, boosters for all might still get the nod. “That’s the beauty of the emergency use authorization,” said Monto, an epidemiologist at University of Michigan. “It can be changed based on changing data.”
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