A group of 18 vaccine experts, including two departing FDA scientists, published a review in The Lancet on Monday arguing that available doses of coronavirus vaccines should be used to reach currently unvaccinated individuals, rather than for booster shots.

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What does the evidence say about booster shots?

In the review, the experts—who include Philip Krause and Marion Gruber, vaccine experts at FDA who announced last month they would be leaving the agency—wrote, "Even in populations with fairly high vaccination rates, the unvaccinated are still the major drivers of transmission."

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Specifically, the authors reviewed a variety of studies from around the world since the delta variant's emergence and found that "none of these studies has provided credible evidence of substantially declining protection against severe disease."

Several studies published by CDC have found that vaccine efficacy against mild infection does wane over time, the New York Times reports. However, the authors wrote that "reductions in vaccine efficacy against mild disease do not necessarily predict reductions in the (typically higher) efficacy against severe disease."

They added, "Even if boosting were eventually shown to decrease the medium-term risk of serious disease, current vaccine supplies could save more lives if used in previously unvaccinated populations than if used as boosters in vaccinated populations."

The experts argued that promoting booster shots unnecessarily could undermine confidence in Covid-19 vaccines, especially if the extra doses carry side effects. Further, if federal authorities approve boosters for only one manufacturer's vaccine but not for others, the result could be widespread public confusion.

"As more information becomes available, it may provide evidence that boosting is needed in some subpopulations," such as the immunocompromised, the authors wrote. "However, these high-stakes decisions should be based on peer-reviewed and publicly available data and robust international scientific discussion."

One point of contention: Data on boosters in Israel

One particular point of disagreement between booster advocates and skeptics has been emerging data from Israel, which recently began offering Covid-19 vaccine boosters to adults over the age of 60.

A pre-print study published earlier this month that found that Israeli adults who received a booster shot of Pfizer-BioNTech's vaccine were 11 times less likely to be infected with the coronavirus 12 or more days post-booster.

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Eric Topol, founder of the Scripps Research Translation Institute, said this constitutes "unequivocal" evidence that booster shots work for Pfizer-BioNTech's vaccine in older populations.

But the 18 vaccine experts in their review in The Lancet cast doubt on the importance of the Israeli data. They said some evidence from studies in the country was collected only a week or so after a booster shot was administered, meaning the effectiveness might not hold up over time. "[A] very short-term protective effect would not necessarily imply worthwhile long-term benefit," they wrote.

For his part, Topol also suggested the authors of The Lancet review had offered a false choice between using vaccine doses for boosters or to reach the unvaccinated.

"This is not about global equity, which the Lancet essay was clearly advancing," Topol wrote on Twitter. "It's not either/or. There are 76 million vaccine doses distributed in the U.S., not given, that are not going to be sent" outside of the United States.

FDA panel to meet Friday

The controversy comes as FDA has scheduled a meeting of a panel of outside experts to discuss Covid-19 booster shots on Friday—just days before the Biden administration has said booster shots could be available to the general public.

The purpose of the public meeting is to consider data on booster shots of the Pfizer-BioNTech vaccine, but the meeting will likely also address other booster-related questions, the Washington Post reports.

Peter Marks, director of FDA's Center for Biologics Evaluation and Research, said "a transparent, thorough, and objective review of the data by the FDA is critical so that the medical community and the public continue to have confidence in the safety and effectiveness of Covid-19 vaccines."

Jason Schwartz, associate professor of health policy and the history of medicine at the Yale School of Public Health, said, "It's a good sign that the FDA is trying to adhere to a regular process."

However, Schwartz added the meeting might be "awkward" since the Biden administration has been criticized for "a really messy sequence of events." (Mandavilli, New York Times, 9/14; AP/Modern Healthcare, 9/13; Herman, Axios, 9/13; Weiland/Mandavilli, New York Times, 9/13; Gardner, Politico, 9/13; McGinley/Diamond, Washington Post, 9/1)