WASHINGTON — The U.S. Food and Drug Administration on Wednesday authorized a booster dose of the Pfizer and BioNTech COVID-19 vaccine for those 65 and older, all people at high risk of severe disease, and others who are regularly exposed to the virus.

The decision paves the way for a quick rollout of the booster shots as soon as this week for millions of people who had their second dose of the vaccine at least six months ago.

“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 for the Pfizer-BioNTech COVID-19 Vaccine 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,” acting FDA Commissioner Janet Woodcock said in a statement.

Pfizer had asked the FDA to expand its vaccine approval to include boosters for all people aged 16 and older and presented data last week to an outside FDA panel of advisers that it said showed waning immunity over time.

CDC Advisory Committee on Immunization Practices is expected to vote Thursday on its own guidelines for use of the shots.