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A third dose of Pfizer's COVID-19 vaccine (Comirnaty) was authorized for use in older adults and high-risk populations, the FDA .

The agency amended Pfizer's emergency use authorization (EUA) for the vaccine to include a third dose at least 6 months following the primary series in adults 65 and older, adults ages 18 to 64 at high risk of severe COVID-19, and adults with "frequent institutional or occupational exposure to SARS-CoV-2" that makes them at high risk for severe disease.

"After considering the totality of the available scientific evidence and the deliberations of our advisory committee of independent, external experts, the FDA amended the EUA [...] to allow for a booster dose in certain populations such as health care workers, teachers and day care staff, grocery workers and those in homeless shelters or prisons, among others," said Acting FDA Commissioner, Janet Woodcock, MD, in a statement.

Last week, the agency's Vaccines and Related Biological Products Advisory Committee (VRBPAC) unanimously recommended a booster dose of the Pfizer vaccine for adults ages 65 and up and for high-risk individuals, via the EUA pathway. The committee overwhelmingly voted against approval of a third dose for all individuals ages 16 and up.

VRBPAC was not impressed with Pfizer's lack of clinical trial data, which was supposed to be the main factor in whether or not to grant approval. The manufacturer submitted safety and immunogenicity data from about 300 adults from phase I and phase II/III trials, including only 12 who were 65 and older.

The committee was concerned with the lack of safety data, particularly in younger individuals, given the potential increased risk of post-vaccine associated myocarditis. Real-world data from Israel that showed benefit with a third dose among older adults ultimately tipped the committee toward an EUA for select high-risk groups, rather than full approval.

"We're grateful for the advice of the doctors, scientists, and leading vaccine experts on our advisory committee and the important role they have played in ensuring transparent discussions about COVID-19 vaccines," said Peter Marks, MD, PhD, director of FDA's Center for Biologics Evaluation and Research, in a statement.

The clinical specifics of the EUA will fall to CDC's Advisory Committee on Immunization Practices, which is slated to meet on Thursday to discuss the appropriate populations where booster doses are indicated.

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