An F.D.A. panel recommended against approving a Pfizer-BioNTech booster for people 16 and older.

An F.D.A. panel recommended against approving a Pfizer-BioNTech booster for people 16 and older.

Another Israeli scientist walked the panel through a new study of health records of more than 1.1. million people over age 60. It found that at least 12 days after the booster, the rates of severe disease were nearly twenty-fold lower among those who received a third Pfizer shot compared to those who did not.

Dr. William C. Gruber, a senior Pfizer vice president in charge of vaccine development, suggested that if the United States does not follow Israel’s lead, it could potentially face more than five million more infections a year among people who received their second dose 10 months earlier, compared to those who got the second shot five months earlier.

“Israel could portend the U.S. Covid-19 future, and soon,” he said.

He said Pfizer’s data shows a third shot elicits a robust antibody immune response that equals or greatly exceeds the response after the second dose. Data also show, he argued, that breakthrough infections among vaccinated Americans are linked more to the ebbing power of the vaccine over time instead than to the Delta variant.

But committee members, including some government officials, appeared deeply skeptical of the Pfizer’s data and Israel’s analyses. Dr. Philip Krause, one of the F.D.A. vaccine experts who authored the medical journal review, criticized Pfizer’s presentation of data that had not been peer-reviewed or evaluated by the F.D.A., arguing that possible problems in the modeling within could understate the vaccine’s efficacy.

Dr. Oliver, the C.D.C. official, questioned attempts to draw a parallel between the United States and Israel, noting that Israel has only nine million residents and is less heterogenous than the United States. Notably, she also said that Israel defines a severe case of Covid-19 more broadly than the United States does, which might help explain why Israel reports more serious breakthrough infections among its vaccinated.

Another C.D.C. official, Dr. Amanda Cohn, asked Israeli officials why the spread of the virus there had recently intensified, despite a broad rollout of boosters. Dr. Alroy-Preis said that the Jewish holidays, together with the start of the school year, had contributed to what she suggested would be a temporary surge in cases.

Committee members also said they were concerned about a paucity of safety data in younger recipients of a booster dose, since studies have shown a higher risk of the heart condition myocarditis in young men who received Pfizer-BioNTech’s vaccine. Several of them asked whether it would be better to wait for a booster vaccine designed specifically to fend off the Delta variant of the virus.

Apoorva Mandavilli and Sheryl Gay Stolberg contributed reporting.

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