An expert committee advising the Food and Drug Administration recommended Thursday that regulators phase out the original versions of the coronavirus vaccines, allowing Americans getting their first shots to receive the updated formulations now used as boosters.

As the advisers endorsed ending one era of the COVID vaccination campaign, they also grappled with its future. FDA scientists described a broad series of possible changes to the country’s vaccination program, all of them aimed at simplifying what had become an elaborate set of inoculation guidelines and at defending against wintertime hospital surges.

Among their proposals was adopting a streamlined dosing schedule for all COVID vaccines, one that would apply to Americans based on their age and health risks. Under that proposal, most adults and children with previous vaccines could receive a single extra COVID shot each fall, while older adults, people with weakened immune systems and unvaccinated children could be given more than one additional dose.

The expert advisers did not vote on that proposal. But they offered an outline for how they wanted federal health officials to consider making the COVID vaccination program more routine, pressing them on how to time boosters for greatest protection and formulate them to best defend against new variants.

Jerry Weir, the director of the division of viral products at the FDA, said, “We think that simplification of the vaccination regimen would contribute to easier vaccine deployment, better communication and improved vaccine coverage.”

Committee members overwhelmingly endorsed that position, saying they hoped to reduce confusion caused by different versions of the vaccines and to boost vaccination rates.

“We can’t keep doing what we are doing,” said Dr. Bruce Gellin, chief of global public health strategy at the Rockefeller Foundation. “This is a good path forward.”

The pandemic’s threat has significantly abated since last winter. A vast majority of Americans have been infected with the virus, been vaccinated or both, federal experts said.

Yet an average of more than 560 Americans a day are still dying from COVID, the highest toll since late August, federal data shows. Many more are suffering the prolonged effects of infections. And Ruth Link-Gelles, a public health researcher with the Centers for Disease Control and Prevention, warned Thursday that those who received the original vaccine formulation many months ago had considerably less protection against hospitalization for COVID than people with bivalent booster doses did.

Only about 40% of adults age 65 and older, and only 16% of people age 5 and older, have received the updated booster shot that was rolled out in September. Experts have said that the doses are most urgently needed by older adults, people with immune deficiencies, pregnant women and those with multiple existing health conditions.

Some experts said Thursday that it was too soon to say whether annual doses were needed as they are for the flu.

“I think we need to see what happens with disease burden,” said Dr. Cody Meissner, the chief of pediatric infectious diseases at Tufts University School of Medicine. “We may or may not need annual vaccination.”

Dr. Archana Chatterjee, dean of the Chicago Medical School, said she welcomed a chance “to really go back to the drawing board, if you will, and look at the science a lot more closely than we were able to do in the face of a deadly pandemic” two years ago.

Several new studies in recent days have reported results that, while riddled with gaps in the data and other uncertainties, the authors said reinforced the benefits of the updated bivalent booster shots. Those vaccines were designed to defend against both the original version of the virus and the BA.5 omicron subvariant that spread across the United States in autumn.

One of them, published in the New England Journal of Medicine, found that the bivalent boosters generated stronger protection than the original formulations of booster shots did.

The bivalent booster was about 62% effective against severe COVID, the study found, compared with the original booster, which was 25% effective. (The study examined the original booster during last summer and the updated booster during autumn.)

Another study, conducted by the CDC, suggested that the updated booster shot performed as well against the newest omicron subvariant, XBB.1.5, as it did against the earlier version of omicron, BA.5. For adults younger than 50, a bivalent booster was 48% effective against COVID infections caused by XBB.1.5, the CDC found, and 52% effective against infections caused by BA.5.

Those results could have been skewed, however, by a number of factors. For example, the results from the CDC study could have been affected by rates of previous infection among participants.

Officials said that factor could not be accurately measured, but how well the bivalent vaccine worked would have been understated, not overstated, as a result. Still, they acknowledged that data on how long the added protection lasted was limited to a few months.

Overall, health officials cast the data as an encouraging sign that the updated boosters were holding up against the latest variants, even though they were designed to counter versions of the virus that started disappearing this winter.

As of November, CDC officials said Thursday, people with a bivalent booster were experiencing a 13-fold reduction in the risk of death from COVID compared with unvaccinated people, and a twofold reduction in the risk of death compared with people who were vaccinated but had not received an updated booster.

Pressed by the expert committee Thursday, FDA scientists also weighed in on the contentious question of whether future updated vaccines should be designed in part against the original version of the virus, as the current bivalent boosters are, or against a new version of the virus. They indicated that future vaccine formulations could be aimed exclusively at new variants, rather than the original version of the virus.

FDA officials told the committee that an extensive investigation had alleviated worries that the updated booster shot made by Pfizer-BioNTech could increase the risk of strokes in people age 65 and older. One surveillance system suggested a possible heightened risk. But federal regulators said other major safety-monitoring systems failed to validate that concern and there was no reason not to recommend the shot.

This article originally appeared in The New York Times.