In a surprising vote, a panel of advisers to the Food and Drug Administration on Friday recommended against approval of a booster dose of the Pfizer-BioNTech COVID-19 vaccine for people 16 years and older.
The 16-2 vote against broad use of the booster, which would be given about six months after completion of the two-dose immunization regimen, dealt a setback to Pfizer and complicates the FDA's approach to boosters.
After a brief intermission following the rejection, FDA officials returned to the meeting with a revised booster question. The panel then voted 18-0 in support of the agency authorizing a booster shot of the vaccine for people 65 and older or at high risk of severe COVID-19.
The FDA then polled the panel members for advice on other groups of people who might be considered for a booster. Though not an official vote, the panel members unanimously supported authorization of a Pfizer booster dose for health care workers or others at high risk of occupational coronavirus exposure.
The agency typically follows the advice of its advisory committees, though it isn't required to.
The Biden administration said in August that it planned to make booster shots available during the week of Sept. 20. That announcement was controversial because it came before the FDA had weighed Pfizer's application and before the Centers for Disease Control and Prevention's own panel of experts on immunization practices could consider the need for boosters.
The rise of the highly infectious delta variant of the SARS-CoV-2 coronavirus and some evidence that the Pfizer vaccine's protection against infections wanes with time are two of the factors that were cited in support of a booster.
But presentations Friday generally showed that the vaccine is still effective in protecting immunized people against severe illness, hospitalization and death in the United States.
Separately, however, an analysis published Friday in the CDC's "Morbidity and Mortality Weekly Report" found that the Pfizer vaccine's protection against COVID-19 hospitalization dropped from 91% during the first 120 days after vaccination to 77% in the days after that.
Over the course of the meeting, speakers from the FDA, Pfizer, the CDC, Israel and the U.K. presented data on the state of the coronavirus pandemic, experience with the Pfizer vaccine and lab tests.
The most direct support for the Pfizer booster came from laboratory work and a clinical study done by Pfizer that involved a little over 300 people.
"The difficulty for the committee is that you're making incredibly important policy decisions very rapidly in a situation of uncertainty," said Jonathan Sterne, a statistician from the University of Bristol who made a presentation to the panel.