The Food and Drug Administration will allow older adults and people at high risk of severe COVID-19 to receive a third dose of Pfizer and BioNTech's coronavirus vaccine, announcing Wednesday night an amended emergency authorization for the shot.
The regulator's decision, which comes as cases, hospitalizations and deaths from coronavirus infections remain at high levels across the country, clears the way for potentially millions of Americans to get booster doses, which are aimed at maintaining immunity for a longer period of time.
Under the authorization, people over 65 years old or who are between 18 and 64 years and more likely to experience worse outcomes from COVID-19 are eligible for a third dose of Pfizer and BioNTech's vaccine, beginning at least six months after their first two doses. People who are frequently exposed to the virus due to their work, such as healthcare workers and teachers, are also eligible to receive a third dose under the FDA clearance.
The authorization does not cover people who received vaccines developed by Moderna or Johnson & Johnson.
All three vaccines remain strongly protective against hospitalization from COVID-19, according to a study published by the Centers for Disease Control on Friday. But other studies have shown weakening efficacy against infection, prompting growing concern among public health officials in the U.S. and other countries. Some, like the U.K., France and Israel have already rolled out booster shot campaigns.
Pfizer initially asked the FDA to clear a booster dose for anyone over 16 years old. But at a back-and-forth meeting Friday, an independent FDA advisory committee of scientists and medical experts questioned whether boosters are needed yet for younger, healthy adults. They also expressed concerns about the relative lack of data on the safety of an additional dose in those groups. In a 16-2 vote against, the committee overwhelmingly opposed broadly recommending boosters for people 16 years or older.
After working with FDA officials to narrow the proposal, though, the committee unanimously voted to support booster doses for older Americans.
"We just can't simply be in a position where we would be vaccinating people every time we think there's a problem," said Stanley Perlman, a professor at the University of Iowa and committee member, in Friday. "We really need to get a better handle on understanding exactly how these vaccines are mediating protection and the durability of that protection."
In a statement on Wednesday's authorization, Janet Woodcock, the acting FDA commissioner, said the regulator would continue to evaluate the safety and effectiveness of a booster dose following Wednesday's authorization.
Hours before the FDA's decision, advisers to the CDC had met to discuss a booster dose and its implementation, dissecting data on the vaccine's efficacy over time and safety in specific groups.
"The idea of vaccinating healthcare workers should be a little bit different than our idea of using vaccines in the general population. It would be to maintain necessary and needed staffing levels because we have large populations that are unvaccinated," said Helen Talbot, a CDC advisory member and professor at Vanderbilt University.
In an unofficial vote Friday, the FDA advisers also said they supported including healthcare workers and others whose jobs put them at higher risk of exposure, a broader category that includes many more Americans. Woodcock, in her statement, gave teaches, daycare staff, grocery workers and those in homeless shelters or prisons as other examples of people would be covered.
The CDC committee is currently scheduled to reconvene on Thursday to vote on recommending the now authorized booster dose.
In making its case to the FDA, Pfizer had emphasized real-world data from Israel, where boosters are available to anyone over 30. The drugmaker also compiled immune response and safety results from several hundred people who had received a third dose in clinical testing.
FDA advisers were concerned, however, about the risk of myocarditis or pericarditis — inflammation in and around the heart — that can occur in rare instances after receiving an mRNA vaccine, particularly in young men. COVID-19 the disease is also associated with myocarditis.
"I have a serious concern about myocarditis and young people," James Hildreth, CEO of Meharry Medical College and a panel member, said. "If it's related to the immune response — and the booster shots induce a very strong response — is that going to amplify the risk for myocarditis in those individuals?"
Another committee member, Hayley Gans of Stanford University called the lack of convincing safety data available at the meeting a "missed opportunity."
The committee's vote Friday upset plans laid out by the Biden administration last month to begin offering booster shots broadly starting on Monday. The administration was responding to concerns of waning protection from vaccines just as the delta variant grips the country, factors that played into Biden's contentious recent decision to mandate vaccination for as many as 100 million Americans.
Moderna has also submitted an application for authorization of a third dose of its coronavirus vaccine, but the FDA is still reviewing the company's data.
Health officials have stressed the need for more data from Johnson and Johnson before considering a booster dose for the company's one-shot regimen. The company is still awaiting results from a study testing a two-dose regimen that could inform any future decision on a J&J booster dose.
On Wednesday, CDC advisers were concerned about how to issue guidance for those who were initially vaccinated with either Moderna's or J&J's. Grace Lee, the CDC committee's chair and a professor at Stanford University's medical school, said she envisions the committee eventually making recommendations applicable to all coronavirus vaccines.
"Over time, my hope is that we don't have to tackle it product by product but rather we can tackle it by population and by what makes common sense and what makes good clinical sense," Lee said.