WASHINGTON — A vaccine advisory committee gathered by the Centers for Disease Control and Prevention on Friday gave a key endorsement for COVID-19 booster doses for all adults, setting up shots to start once the head of the agency signs off.

The panel unanimously voted to allow all adult recipients of the Pfizer and Moderna COVID-19 vaccines to receive a booster dose at least six months after their second shot. The group gave a stronger endorsement to people ages 50 and older, saying they should get a booster instead of saying they “may” get the shot.

CDC Director Rochelle Walensky is expected to promptly sign off on the recommendations, formally allowing the shots to begin. The Food and Drug Administration authorized the shots on Friday without convening its vaccine advisory committee, saying that it “concluded that the requests do not raise questions that would benefit from additional discussion by committee members.” Johnson & Johnson recipients were already eligible for a booster shot.