Ahead of the holidays, a C.D.C. panel is set to weigh Pfizer-BioNTech and Moderna boosters for all adults.

After weeks of contradictory statements and confusing guidelines about which Americans need booster shots of coronavirus vaccines, federal health officials are poised to recommend them to everyone over 18.

An advisory panel to the Centers for Disease Control and Prevention is scheduled to meet on Friday to weigh the pros and cons of recommending the boosters to all adults. But the discussion is not expected to turn up any surprises, and the final recommendations from the agency itself are likely to align with President Biden’s promise that all adults would be eligible for extra doses. The meeting is to begin at 12 p.m. Eastern time.

Desperate to dampen even a dim echo of last winter’s horrors, the Biden administration is betting that booster shots will shore up what some have characterized as waning immunity among the fully vaccinated. The Food and Drug Administration authorized boosters of the Pfizer-BioNTech and Moderna vaccines for all adults on Friday.

Research suggests that the shots may help forestall at least some infections, particularly in older adults and those with certain health conditions.

After an all too brief respite, coronavirus infections are inching up again, particularly in parts of the country where cooler weather is hustling people indoors.

The C.D.C.’s decision will land just as Americans are poised to travel, likely in record numbers, to spend the holidays with family and friends. Given the roughly 100 million Americans who have yet to receive a single dose of vaccine, holiday travel and get-togethers could send cases skyrocketing, as they did last year.

Several European countries are also offering boosters to all adults in a bid to contain fresh waves of infections. France has gone so far as to mandate booster shots for those over age 65 who wish to get a health pass permitting access to public venues.

“Look what other countries are doing now about adopting a booster campaign virtually for everybody,” Dr. Anthony S. Fauci, the Biden administration’s top Covid adviser, said at a conference on Tuesday. “I think if we do that, and we do it in earnest, I think by the spring we can have pretty good control of this.”

But many experts, including some who advise federal agencies, are skeptical that boosters alone can turn the tide. While the extra shots can strengthen immunity in older adults, they are unlikely to offer much benefit to adults under 65, who remain protected from severe illness and hospitalization by the initial immunization, the experts said.

It is also unclear whether booster shots can significantly slow the spread of the virus. The limited evidence available suggests that vaccines can blunt transmission, but only to a limited extent and for a limited period.

Many pandemic-weary Americans, too, seem unmoved by the administration’s push for boosters. More than 85 percent of the adult population is already eligible, but only about 17 percent has chosen to get them. And those may not be the people most in need of extra protection.

As with the initial shots, fully vaccinated white people are more likely to have lined up for a booster shot, compared with other racial and ethnic groups, according to data compiled by the Kaiser Family Foundation.

So far, the people who have opted for boosters “tend to be of higher socioeconomic status and more highly educated, and have more access in general to medical care,” said Dr. Celine Gounder, an infectious disease specialist at Bellevue Hospital Center.

“That’s not necessarily who’s actually at risk of severe disease, hospitalization or death, and so I think you’re going to have limited public health impact.”