In Review, Top F.D.A. Scientists Question Imminent Need for Booster Shots

WASHINGTON — Two departing Food and Drug Administration regulators argued in a review published Monday that none of the data on coronavirus vaccines so far provided credible evidence in support of booster shots for the general population. Their assertion revealed significant disagreement between career scientists at the agency and top Biden health officials, who have already started planning a broad booster campaign for this fall.

The review, published in The Lancet, was written by an international group of vaccine experts including Dr. Philip Krause and Marion Gruber, longtime F.D.A. scientists who recently announced that they would leave the agency. It comes days before an advisory committee is to publicly discuss and vote on whether the F.D.A. should approve additional doses of Pfizer-BioNTech’s vaccine for people 16 and up.

Dr. Krause and Dr. Gruber, who lead the F.D.A.’s vaccine office and have regulated vaccines for decades, were not writing on behalf of the agency; the article stated that “opinions expressed are those of the authors, and do not necessarily represent the opinions of their respective organizations.” Still, the arguments they put forth suggested that regulators might raise objections to Pfizer’s application for approval of a booster dose at the advisory panel meeting, scheduled for Friday.

An F.D.A. spokeswoman emphasized that “the views of the authors do not represent the views of the agency,” adding: “We are in the middle of a deliberative process of reviewing Pfizer’s booster shot supplemental approval submission, and F.D.A. as a matter of practice does not comment on pending matters before the agency. We look forward to a robust and transparent discussion on Friday about that application.”

Dr. Gruber and Dr. Krause were said to have disagreed with the Biden administration’s push for boosters before federal scientists could review all the evidence and make recommendations, a conflict that factored into their decisions to depart this fall. The two are likely to be crucial to any decisions the agency makes about boosters; Dr. Gruber would be expected to formally sign off on them.

But other top F.D.A. officials, including Dr. Janet Woodcock, the acting agency commissioner, and Dr. Peter Marks, a career regulator who oversees the vaccine office that Dr. Gruber and Dr. Krause lead, could overrule them.

The publication of the Lancet article raised questions about whether Dr. Woodcock, who signed on to the Biden administration’s booster announcement last month, had consulted Dr. Gruber or other career experts in the F.D.A. vaccine office before advising the administration and making clear her own position on the issue. Some public health experts said Dr. Woodcock’s endorsement of the plan boxed in her regulators.

The Biden administration announced in August a proposal to begin administering vaccine boosters eight months after people’s second shots, contingent on authorization from the F.D.A. and a recommendation from the Centers for Disease Control and Prevention. And the pandemic plan that Mr. Biden announced last week included booster-shot readiness, stating, “A booster promises to give Americans their highest level of protection yet.”

But many scientists have opposed the plan, saying the vaccines continue to be powerfully protective against severe illness and hospitalization. The authors of the Lancet articleincluded a compendium of dozens of studies from around the world that shows such a trend.

Federal health officials have said that one reason they announced the booster plan was to stay ahead of the virus and be ready for when vaccines may no longer protect as well against severe cases of Covid-19. Those officials, including Dr. Anthony S. Fauci, Mr. Biden’s chief medical adviser, have relied heavily on data presented to them by Israeli officials, who have defended that country’s early, aggressive booster campaign.

Their data, Dr. Fauci and other administration officials have said, show a clear waning of immunity against infection, with enhanced protection from booster doses, but show only hints of waning immunity against hospitalization in people under 65.

But in the new review, Dr. Krause, Dr. Gruber and other vaccine experts said that more time and public discussion, and better studies, were needed to determine if boosters were needed for the general population. They also said that whatever advantage the shots might provide would not outweigh the benefit of using them to protect the billions of people who remain unvaccinated worldwide.

The World Health Organization has asked wealthy countries to hold off on administering extra shots to healthy patients until at least the end of the year as a way of enabling every country to vaccinate at least 40 percent of its population. Every unvaccinated person provides an opportunity for the virus to morph into new, potentially dangerous, variants, scientists have warned.

The review authors did, however, say that extra shots might be useful for some people with weak immune systems — a step the F.D.A. already authorized.

“As more information becomes available, it may first provide evidence that boosting is needed in some subpopulations,” they wrote. “However, these high-stakes decisions should be based on peer-reviewed and publicly available data and robust international scientific discussion.”

They were largely dismissive of the Israeli data and other studies that some health officials have said make the case for imminent extra shots. They said some Israeli evidence was collected just a week or so after the third dose and might not hold up over time, and that “a very short-term protective effect would not necessarily imply worthwhile long-term benefit.”

They also said that a reduction in vaccine efficacy against mild cases of Covid-19 did not necessarily mean there would be a drop in efficacy against severe disease.

“To date, none of these studies has provided credible evidence of substantially declining protection against severe disease,” they wrote, “even when there appear to be declines over time in vaccine efficacy against symptomatic disease.”

The authors also said that countries with a lot of vaccinated people would inevitably see some breakthrough cases, especially if the vaccinated start taking more risks.

Several studies published by the C.D.C., including three on Friday, suggest that while efficacy against infection with the Delta variant seems to wane slightly over time, the vaccines hold steady against severe illness in almost all age groups. Only in adults over 75 do the vaccines show some weakening in protection against hospitalization.

Immunity conferred by vaccines relies on protection both from antibodies and from immune cells. Although the levels of antibodies may wane and raise the risk of infection, the body’s memory of the virus is long-lived.

The vaccines are slightly less effective against infection with the Delta variant than with the Alpha variant, but the virus has not evolved to evade the sustained responses from immune cells, the experts said. Boosters may eventually be needed even for the general population if a variant emerges that sidesteps the immune response, they added.

The experts cautioned that promoting boosters before they are needed, as well as any reports of booster side effects such as heart problems or Guillain-Barré syndrome, might undermine confidence in the primary vaccination. They wrote that because booster doses have been shown to induce strong responses, lower doses might be adequate and safer. They also emphasized that tweaking the vaccines to specifically protect against new variants, like Delta, might be the best and longest-lasting approach, in part because new variants would be likely to evolve from those in highest circulation. Moderna and Pfizer are both evaluating Delta-specific booster shots.

The F.D.A. is still gathering data on all three vaccines used in the United States, and it will be at least several weeks before regulators can decide whether people who received the Moderna or Johnson & Johnson vaccines might need another dose. Starting boosters for recipients of only one vaccine could confuse the public, the authors said.

“Booster programs that affect some but not all vaccinees may be difficult to implement — so it will be important to base recommendations on complete data about all vaccines available in a country, to consider the logistics of vaccination, and to develop clear public health messaging before boosting is widely recommended,” the authors wrote.