Publisher Health

WASHINGTON — The Biden administration plans to offer the next generation of coronavirus booster shots to Americans 12 and older soon after Labor Day, a campaign that federal officials hope will reduce deaths from Covid-19 and protect against an expected winter surge.

Dr. Peter Marks, the top vaccine regulator for the Food and Drug Administration, said in an interview on Tuesday that his team was close to authorizing updated doses that would target the versions of the virus now circulating.

Even though those formulations have not been tested in humans, he said, the agency has “extremely good” data showing that the shots are safe and will be effective. “How confident am I?” he said. “I’m extremely confident.”

This week, both Moderna and Pfizer-BioNTech finalized their submissions to the F.D.A. asking for emergency authorization of booster shots aimed at BA.5 and another subvariant of Omicron that together account for most coronavirus cases in the United States.

Federal health officials say they are eager to offer the updated boosters as quickly as possible, pointing to a death toll that now averages about 450 Americans per day and could rise in the coming months as people spend more time indoors.

“We have really got to do better to protect the American public,” Dr. Anthony S. Fauci, President Biden’s chief medical adviser, said in an interview on Tuesday. “We are in the middle of a BA.5 outbreak here, and we are nowhere near where we want to be.”

The Biden administration has struggled to convince Americans of the need for successive vaccinations. Only about two-thirds of the population has been inoculated with the primary series of two shots, and far fewer have received booster doses.

Some outside scientists have said the government is moving too fast to clear redesigned shots, saying that the existing vaccines provide strong protection against severe disease.

“Deaths are concentrated in unvaccinated people and people with serious health conditions,” said John P. Moore, a virologist at Weill Cornell Medicine. He said the protection that the new shots provided against infection could be “weak to nonexistent.”

Jeremy Kamil, a virologist at Louisiana State University Health Shreveport, said that although he supported new boosters, many people had immunity from recent infections. “Even if we get this out in the next 10 days, how many people are left who haven’t gotten Omicron?” he said.

Other scientists said that the government’s plan made sense given how the virus has changed. Dr. Marks said that if regulators waited for additional data or recommendations from outside experts, the virus might evolve further and “we may have lost a bunch of individuals who could otherwise be sitting around at the dinner table together.”

In a sign of impending action from the F.D.A., the Centers for Disease Control and Prevention has scheduled a two-day meeting of its advisory panel of experts on the matter for Sept. 1 and 2. The C.D.C. director, Rochelle P. Walensky, would then make a final decision on whether to roll out the new doses. Shipments to states could begin as early as next week.

Officials plan to offer the new Pfizer booster to everyone 12 and older while limiting the new Moderna shot to adults. People who have already received the initial two-shot series of either vaccine would be eligible. So would those who have received the initial shots plus one or two booster shots. The new booster campaign could be broadened to younger children later.

Dr. Marks said the F.D.A. might want people who have recently received a Covid vaccine dose to wait “a few months” before getting the new shot. He said the C.D.C. might weigh in on whether people who were recently infected with the virus should also wait.

As of mid-August, the federal government had bought more than 170 million doses of the updated version of the vaccines. This month, the C.D.C. laid out detailed plans to offer the shots, warning that the supply would be “sufficient but finite” and saying that doses should be “directed to providers with expected demand among eligible patients.”

The new shots combine the original vaccine with components aimed at the BA.4 and BA.5, Omicron’s recent subvariants. Officials argue that the new formulations will deliver a stronger boost to the immune system than the existing vaccines provide.

Unlike earlier shots, the redesigned formulations have not been tested widely on humans; instead, the companies have submitted data from mice trials. Some vaccine experts have complained that animal data is too preliminary and regulators should wait for results of trials with human volunteers.

But Dr. Fauci said using such data was “not anything different than we always do” in updating the flu vaccine each year. And Dr. Marks said the evidence includes the existing vaccines’ extensive track record and a series of earlier human trials with variant-specific formulations.

“I take great issue with those who say, ‘Oh, you’re just approving this with mouse data,’” he said. “We’re authorizing this with the totality of the evidence that we have.”

Moderna and Pfizer have both submitted clinical data from human studies of redesigned shots targeting the original version of the Omicron variant. Britain last week authorized that version of Moderna’s vaccine, but U.S. regulators asked for formulations aimed at the newer subvariants.

Researchers are still working to answer key questions about the protection that the new vaccines deliver, including the levels of antibodies the shots generate in humans and how those antibodies protect people. Moderna began human trials of its new vaccine this month, and Pfizer plans to do the same later in the month. Initial data from those trials is expected later this year.

Dr. Moore, the virologist at Weill Cornell Medicine, said the administration’s plans could backfire if the fall or winter brings a wave of disease despite the new formulations, potentially reducing overall confidence in Covid-19 vaccines.

“My issue all along has been: Is there enough data to really justify the effort?” Dr. Moore said. “The potential downside is, if the public thinks that this Omicron-containing booster is some kind of magic bullet that will give them super strong protection from infection, is there a risk that they will change their behavior to increase their exposure?”

The F.D.A. will decide whether to authorize the retooled doses without seeking a recommendation from its outside advisory panel of experts, a step it usually takes before making new vaccines available. Critics have complained that regulators have bypassed the panel at crucial steps.

Dr. Marks defended the decision, saying a late June meeting of the advisory panel on the need to update the vaccines had given regulators “everything we needed.” The committee voted overwhelming then to recommend that the vaccines be updated for Omicron, but it did not consider specific formulations.