WASHINGTON — An expert panel recommended Tuesday that the Food and Drug Administration move to updated coronavirus booster shots targeting a form of the Omicron variant that has dominated for months.

The panel’s vote clears the way for the FDA to push manufacturers to make reformulated boosters in time for the Biden administration to offer them later this year, ahead of an expected winter surge of the virus.

The decision came after a day of thinking about where the virus is heading and how best to tackle it. A senior FDA official called it “science at its toughest.” One committee member described the data as “uncomfortably sparse”.

And a senior official from one of the vaccine makers, Moderna, told the panel that his company would not be able to manufacture the kind of doses that regulators seem to be favoring until late October or early November. assuming “no data to assess the vaccine at all”.

“None of us have a crystal ball” Dr. Peter Marks, a senior FDA regulator who oversees the agency’s office of vaccines, said. “If you do, come to my house right away. I would really like that.

Despite all the uncertainties, the panel fell 19-2 in favor of revamping the booster shots to also target Omicron or its subvariants, rather than just the original version of the virus.

“We are all troubled by the steady erosion of immune protection,” said Dr. Mark Sawyer, an infectious disease specialist at the University of California, San Diego School of Medicine. “We’re going to be behind the eight ball if we wait any longer.”

The committee debated but did not specify which wording might work best. The FDA was clearly leaning towards a combination of the existing vaccine and a vaccine adapted to two subvariants of Omicron, BA.4 and BA.5. According at new estimates from the Centers for Disease Control and Preventionthese subvariants now form more than half of new cases in the country.

It would be a rejection of the booster candidates that Pfizer and Moderna, the two main vaccine developers, have manufactured in the hope that the government will buy doses. The companies had opted for a combination of the existing vaccine and a vaccine that targets Omicron itself, not its subvariants.

But Omicron was squeezed out by subvariants nearly three months ago, and regulators said in the information documents that a recall targeting him would be “already a bit outdated”.

The committee’s recommendation is not binding, but a no would have dealt a blow to the Biden administration’s efforts to update existing boosters by the fall. Dr Marks suggested the agency would follow up with its own recommendation “very quickly”. With recall contracts worth billions at stake, manufacturers are expected to follow the wishes of regulators.

The meeting highlighted scientific angst over how to combat a virus that is moving faster than clinical trials involving humans can yield results. The panel ignored the contentious question of who should be eligible for a drop recall.

“Right now, the bottom line is that manufacturers need to know what to put in their vaccine,” Dr Marks said. “Over the next few months, I think we will have an idea, and there will be plenty of time to debate who is more suitable for boosters.

He predicted that older Americans, at least, might need the next round of protection — a strategy that even some of the more skeptical committee members favor.

Committee members advocated for continuing to use existing vaccines for people who have not yet received the first shots. “I don’t think we should lose the prototype,” said Dr. Amanda Cohn, a senior CDC official. “I think it’s a well-known entity and is doing very well in its current job.”

But some panelists questioned whether Moderna and Pfizer, along with partner BioNTech, came up with the best booster candidates. Many have said that Novavaxa company whose vaccine isn’t even available for initial doses in the United States yet, presented more impressive data.

Dr. Bruce Gellin, panel member and head of global public health strategy at the Rockefeller Foundation, called for stronger federal leadership. “We need to have better central coordination, not just for these studies, but for what the plan is going forward,” he said.

Little was said about a variant except for Omicron, which turned out to be a worldwide game changer.

Jerry Weir, a senior FDA regulator, said Omicron and its offshoots have been dominant for about six months now, and whatever the next incarnation of the virus is, it’s more likely to be related to the Omicron family. than in previous versions.

Federal health officials have repeatedly suggested that more advanced vaccines may be needed. As vaccine-induced protection against infection has waned, some Americans have been reinfected even within several months.

In briefing documents, FDA officials said the risk of another major outbreak would increase later this year “due to the combination of waning immunity, new variant evolution, and increased inner activity”.

Justin T. Lessler, an epidemiologist at the University of North Carolina at Chapel Hill, presented a series of disturbing projections about the US trajectory of the virus. In the most optimistic scenario, his team predicted 95,000 deaths in the 12-month period ending in March 2023. In the most pessimistic scenario, the nation would see more than 200,000 deaths.

While the committee largely agreed that a drop booster should be reconfigured to target the Omicron family, exactly how was much less clear. Dr. Adam C. Berger, a National Institutes of Health official, voted in favor of an updated recall, but said: “I’m not sure we have the evidence to support a change necessarily today. .”

Dr Kanta Subbarao, an adviser to the World Health Organization who came to the committee, said she and her colleagues believe a combination of the original vaccine and an Omicron targeting alone could provide a range wider protection and avoid the scramble to keep up with the most common variants. The companies presented data showing that such a formulation increased the level of neutralizing antibodies more than the existing booster, but less than doubled, with only a short follow-up period.

Other experts on the panel said they preferred instead to target the BA.4 and BA.5 subvariants that have become the dominant forms of the virus in the United States. Pfizer presented the only data on such a formulation.

A company official said preliminary data from a mouse trial showed it worked better against all Omicron subvariants than the existing vaccine. She said the researchers don’t yet have a side-by-side comparison with a booster targeting Omicron itself.

If regulators choose the subvariant option, it will be particularly difficult to deliver doses on time.

Kathrin Jansen, head of vaccine research at Pfizer, said whichever formulation the FDA chooses, “we’re ready” to deliver doses in early October. But Dr Stephen Hoge, chairman of Moderna, said his company would only be able to deliver in late October or early November – and only “assuming no clinical data requirements”.

Dr. Weir said that although it is difficult to draw general conclusions from different studies conducted by different companies, overall the data indicates that a booster that incorporates an Omicron component produces a better antibody response against this family of viruses. This offers “the potential for improving the effectiveness of vaccines”, he said.