A federal advisory panel assembled by the U.S. Food and Drug Administration overwhelmingly rejected a plan Friday to offer Pfizer booster shots against COVID-19 to most Americans.

The vote by the committee of outside experts was 16-2, with committee members expressing frustration that Pfizer had provided little data on the safety of extra doses. Many also raised doubts about the value of mass boosters, rather than ones targeted to specific groups.

The rejection operates contrary to the Biden administration's sweeping plan, proposed one month ago, to offer booster shots of both the Pfizer and Moderna vaccines to nearly all Americans eight months after they get their second dose.

Both FDA leaders and the panel indicated they would take a second vote Friday afternoon on recommending the booster shots for older Americans and other high-risk groups.

The second vote was 18-0, endorsing emergency approval for the booster shot at least six months after the second dose for people ages 65 and older and those at high risk of occupational exposure and severe COVID-19.