By Lauran Neergaard and Mike Stobbe

AP Medical Writers

The U.S. vaccination drive against COVID-19 stood on the verge of a major new phase as government advisers Thursday recommended booster doses of Pfizer’s vaccine for millions of older or otherwise vulnerable Americans — despite doubts the extra shots will do much to slow the pandemic.

Advisers to the Centers for Disease Control and Prevention said boosters should be offered to people 65 and older, nursing home residents and those ages 50 to 64 who have risky underlying health problems. The extra dose would be given once they are at least six months past their last Pfizer shot.

Deciding who else might get one was far tougher. While there is little evidence that younger people are in danger of waning immunity, the panel offered the option of a booster for those ages 18 to 49 who have chronic health problems and want one.

The advisers refused to go further and open boosters to otherwise healthy front-line health care workers who aren’t at risk of severe illness but want to avoid even a mild infection.

“We might as well just say give it to everyone 18 and older. We have a very effective vaccine and it’s like saying, ‘It’s not working.’ It is working,” said Dr. Pablo Sanchez of Ohio State University, who helped block the broadest booster option.

Still, getting the unvaccinated their first shots remains the top priority, and the panel wrestled with whether the booster debate was distracting from that goal.

All three of the COVID-19 vaccines used in the U.S. are still highly protective against severe illness, hospitalization and death, even amid the spread of the extra-contagious delta variant. But only about 182 million Americans are fully vaccinated, or just 55% of the population.

“We can give boosters to people, but that’s not really the answer to this pandemic,” said Dr. Helen Keipp Talbot of Vanderbilt University. “Hospitals are full because people are not vaccinated. We are declining care to people who deserve care because we are full of unvaccinated COVID-positive patients.”

Thursday’s decision represented a dramatic scaling back of the Biden administration plan announced last month to dispense boosters to nearly everyone to shore up their protection. Late Wednesday, the Food and Drug Administration, like the CDC panel, signed off on Pfizer boosters for a much narrower slice of the population than the White House envisioned.

It is up to the CDC to set final U.S. policy on who qualifies for the extra shot. A decision from the agency was expected later Thursday, but the CDC usually follows its advisers’ recommendations.

The booster plan marks an important shift in the nation’s vaccination drive.

CDC Director Dr. Rochelle Walensky opened Thursday’s meeting by stressing that vaccinating the unvaccinated remains the top goal “here in America and around the world.”

Recommendations will   change if evidence shows more people need a booster.