Publisher Health

WASHINGTON — The Food and Drug Administration is planning to broaden eligibility for coronavirus vaccine booster shots on Monday, allowing 12- to 15-year-olds to receive third doses of Pfizer-BioNTech’s vaccine, according to people familiar with the agency’s deliberations.

Regulators are also expected to authorize an extra shot of Pfizer’s vaccine for both adolescents and adults five months after receiving a second dose, instead of the current interval of six months. Younger children, ages 5 to 11, with immune deficiencies would be able to receive booster shots as well.

The decision to expand the use of the shots would come just as schools begin to reopen after the holiday break, and as governments around the world try to respond to the fast-spreading Omicron variant. Israel on Thursday approved a fourth dose of vaccine for people with weakened immune systems, and Britain’s National Health Service said its hospitals would erect field wards to help deal with the surge in coronavirus cases.

Several U.S. states hit their all-time case records for the coronavirus this week, disrupting the lives of millions of Americans. New York’s mayor-elect, Eric Adams, vowed to keep the city’s vaccine mandate for private-sector employees in place, and the C.D.C. issued a blunt warning to potential travelers: “Avoid cruise travel regardless of vaccination status.”

Health officials are trying to encourage more Americans to get a booster shot — just over a third of fully vaccinated adults have received one — and warn that the unvaccinated face the greatest risk of severe illness and death from Omicron.

“Our C.D.C. guidance has been very clear that people should get their boost when they are eligible,” Dr. Rochelle P. Walensky, the C.D.C. director, told reporters this week. “That is both for — because of waning immunity and because we need more protection against Omicron.”

Dr. Walensky said on Wednesday that even as daily case counts had climbed by roughly 60 percent in the past week, hospitalizations and deaths were still relatively low, a suggestion that Omicron might be less lethal. She and Dr. Anthony S. Fauci, President Biden’s chief medical adviser, cited international research hinting at the same conclusion.

Studies have shown that while two doses of the Pfizer-BioNTech vaccine have provided strong protection as the Delta variant swarmed the country, Omicron can evade the defenses of fully vaccinated people, heightening fears about the risks for young people.

More than 70 percent of people 12 and older in the United States are fully vaccinated, according to the C.D.C. Around a quarter of children between 5 and 11 have received at least one dose. Children under 5 are still not eligible for a vaccine.

The latest surge has caused a concerning rise in hospitalizations among children. But early data suggests that Omicron appears to be causing milder illness for children, similar to findings for adults. And hospital officials and physicians have said that nearly all children hospitalized with Covid-19 were unvaccinated or partially vaccinated.

Children can better withstand coronavirus infections, but in rare instances can still become very sick and even die. At least 1.8 million adolescents between 12 and 15 years old have tested positive for the virus, according to the C.D.C.

A series of studies published on Thursday by the agency underscored how important vaccination can be for children and adolescents. In one study spanning July through early December that examined hundreds of adolescents in Arizona, researchers said two doses of the vaccine reduced the risk of infection by 92 percent.

Two other C.D.C. studies showed that there were few serious side effects reported among 5- to 11-year-olds who had received the Pfizer-BioNTech vaccine, and that pediatric hospitalizations occurred mostly among children who had not been fully vaccinated.

One recent South African study showed that the effectiveness of Pfizer’s vaccine against severe illness and hospitalization was about 70 percent after two doses, against Omicron in particular.

Pfizer-BioNTech’s vaccine is the only of the three federally authorized coronavirus shots that is approved for use in people under 18.

The Centers for Disease Control and Prevention’s vaccine advisory committee is planning to meet by the middle of next week to weigh in on whether to recommend the changes in the F.D.A.’s booster policy. If the committee agrees with the F.D.A.’s authorizations, Dr. Walensky is expected to promptly endorse the revisions.

Dr. Kathryn M. Edwards, a vaccine expert and professor of pediatrics at Vanderbilt University School of Medicine, said the F.D.A.’s expected decision was justified.

“We’re having a lot of suggestions and a lot of experience with Omicron that it’s infecting people that have been boosted. But fortunately, we’re not seeing a lot of severe disease,” she said. “So I think if you look at the immune responses, at least in adults, you’ll see that this booster dose does enhance your neutralization capacity against Omicron.”

Other vaccine experts said the administration’s continued attention to offering boosters to younger, healthier people was misguided.

Dr. Paul Offit, the director of the Vaccine Education Center at Children’s Hospital of Philadelphia and a member of the F.D.A.’s vaccine advisory committee, said research on vaccine effectiveness, including against Omicron, had revealed substantial and durable protection from two doses against severe disease, including in adolescents — the purpose of vaccination, he said.

A booster dose could increase one’s protection for several months, he said, but delivering extra shots to young Americans was “focusing on the people who are already protected.”

The Biden administration, he added, should instead direct more attention to reaching the unvaccinated, a point he said was backed up by the overwhelming majority of hospitalized children he had seen in Philadelphia being unvaccinated.

The F.D.A. had hoped to announce its decision to broaden boosters for children as early as Thursday, the people familiar with the deliberations said, but agreed to wait until Monday because Dr. Walensky said she wanted to hear recommendations from her agency’s outside advisory group before signing off on the changes. That group, which has met throughout the pandemic to consider F.D.A. decisions around vaccines, might not meet until Wednesday.

The two agencies share responsibility for setting the nation’s vaccine policy and have worked to present a unified front in their reviews of booster shots. But the F.D.A. has been more willing to act without the advice of its outside advisory committee, with some top officials arguing that the agency needs to respond as quickly as possible in the face of the public health crisis.

Although the F.D.A. convened its outside advisory committee repeatedly this year, it has not asked the panel for recommendations before its most recent decisions to expand boosters.

Dr. Walensky this month endorsed offering Pfizer-BioNTech booster shots to 16- and 17-year-olds without convening her agency’s expert committee. But she was unwilling to do that for younger adolescents, people familiar with the government’s deliberations said.

Some outside experts have argued that in bypassing the outside committees, the C.D.C. and the F.D.A. were wrongly limiting public discussion about the evidence to justify expanding the use of boosters.

Dr. Offit said a meeting of the F.D.A. committee, which had initially been skeptical about younger, healthy people needing booster doses, to discuss the most recent booster decision could offer some transparency about the data that regulators reviewed.

“The American public gets to hear that discussion,” he said.

Federal regulators based their decision at least in part on data from Israel that showed no serious safety concerns in thousands of 12- to 15-year-olds who received a third dose of the Pfizer vaccine. There were no reports of myocarditis, a rare side effect seen mostly in younger men that has been linked to the Pfizer and Moderna vaccines. The condition involves inflammation of the heart muscle.

The F.D.A. wants to allow a booster shot as early as five months after the second Pfizer dose in part because Israeli data suggests that the shorter interval is effective, according to people familiar with the government’s deliberations.

Israel introduced an early and aggressive booster campaign this year, and Biden administration health officials have leaned heavily on the research of Israeli officials to make the case for Americans getting boosters.

Pfizer and BioNTech, its German partner, have both said their studies show that a third dose is needed to raise neutralizing antibodies back to a level that is considered strongly effective against infection. Dr. Albert Bourla, Pfizer’s chief executive, said this month that while two doses may still prevent severe disease from Omicron, a third strengthens protection.

Dr. Ugur Sahin, the chief executive of BioNTech, said three doses “could still offer a sufficient level of protection from disease of any severity” caused by the variant.

Carl Zimmer contributed reporting.