“In our hearts, I think people don’t quite agree with this notion of a booster dose,” said one leading vaccine expert.

In interviews last week, several advisers to the Centers for Disease Control and Prevention and to the Food and Drug Administration said data show that, with the exception of adults over age 65, the vast majority of Americans are already well protected against severe illness and do not need booster shots.

But some said they felt compelled to vote for the shots because of the way the federal agencies framed the questions that they were asked to consider.

Other committee experts said that they wanted to avoid confusing the public further by dissenting, or that they voted according to their views of the evidence and were simply overruled.

also advised last week that people in certain high-risk groups who got one type of Covid-19 vaccine could choose a different one for their booster.

Daley both voted in favor of booster shots at their committee’s meeting on Thursday, but with reservations over how the decision would be viewed by anxious Americans who might conclude mistakenly that the vaccines are ineffective.

committee reviewed evidence for the Pfizer-BioNTech booster in September, the advisers agreed unanimously only on extra shots for adults over age 65.

In interviews, the experts bemoaned the limited data on the safety and efficacy of the booster shots.

Still, some said they felt they had to vote in favor of booster shots of the Moderna and Johnson & Johnson vaccines because they had already recommended boosters of the Pfizer-BioNTech vaccine and did not want to deny other Americans.

But several panelists who did not wish to speak on the record said privately that the final recommendations for booster shots were inevitable as soon as President Biden promised them to all adults.

has authorized booster shots for millions of recipients of the Pfizer-BioNTech, Moderna and Johnson & Johnson vaccines.

Pfizer and Moderna recipients who are eligible for a booster include people 65 and older, and younger adults at high risk of severe Covid-19 because of medical conditions or where they work.

Eligible Pfizer and Moderna recipients can get a booster at least six months after their second dose.

has updated its authorizations to allow medical providers to boost people with a different vaccine than the one they initially received, a strategy known as “mix and match.” Whether you received Moderna, Johnson & Johnson or Pfizer-BioNTech, you may receive a booster of any other vaccine.

says the Covid vaccine may be administered without regard to the timing of other vaccines, and many pharmacy sites are allowing people to schedule a flu shot at the same time as a booster dose.

In some cases, committee members said they voted one way or another simply because of the way those questions were phrased.

advisers evaluated the Pfizer-BioNTech vaccine for people ages 16 and older, the evidence for its use in 16- and 17-year-olds was limited.

advisers said they wanted to recommend that Johnson & Johnson recipients have the option to choose any vaccine for their booster.

only asked the panel to vote on a booster of the Johnson & Johnson vaccine.

Stanley Perlman, said he voted yes because it was clear that Johnson & Johnson recipients would benefit from a second shot.

But the unanimous vote signaled far more confidence in the Johnson & Johnson vaccine as a booster than he felt, said Dr.

Perlman said he was opposed to boosters for younger people at first, but voted in favor for other reasons.

“They continue inadvertently to damn the vaccine, when what they should say is, ‘It is remarkable,’” said Dr