F.D.A. Panel Explores Challenges of Revamping Coronavirus Vaccines

WASHINGTON — Researchers trying to devise an updated coronavirus vaccine for use this fall would have to settle on a formula as early as June to meet that deadline, federal officials said on Wednesday, even though some clinical trials are just now getting underway.

The assessment came during a daylong meeting of outside advisers to the Food and Drug Administration, who convened to strategize about what the nation’s coronavirus vaccine policy should look like moving forward. The session underscored how deeply the road ahead is studded with uncertainties.

Among the most basic questions debated: At what point would officials decide that the existing vaccines are not working well enough? And if better vaccines are deemed necessary, when might clinical trials provide answers about suitable replacements?

The meeting captured a transition point for the Biden administration as it tries to fashion a vaccine strategy for the rest of this year. Some federal health officials are convinced that the existing vaccines need to be retooled to offer better protection than they do now. They hope to have a revised version by the fall, when they fear the virus could resurge in force.

Doses of modified vaccine could cost the federal government about $5 billion to $12 billion, one senior federal official said. Congress has moved to slice the administration’s new Covid budget request roughly in half, which the official said might not leave enough to cover that cost.

At the same time, vaccine manufacturers and federal researchers are scrambling to figure out what a revised vaccine should look like. A new study by the National Institutes of Health, for example, is analyzing how Moderna’s vaccine works if revised to target three different variants, alone or in combination. But it only just began recruiting volunteers, with results expected sometime this summer.

Robert Johnson, the director of an infectious disease division within the Department of Health and Human Services, told the panel that even once regulators decide upon a reconfigured vaccine, manufacturers would need several months to produce doses.

“If you’re not on your way to that clinical trial by the beginning of May, it is very difficult to have collectively across manufacturers enough product to meet that demand” by fall, he said. Dr. Peter Marks, who oversees vaccine regulation at the F.D.A., also described the time frame as highly compressed, saying regulators may need to settle on a new vaccine formula by May or June if they want to switch from the existing ones.

The trials underway are too small to provide efficacy data of the type that led to the authorization of the existing vaccines. But they could produce enough data for federal health officials to determine whether a reconfigured vaccine will create a stronger or more lasting immune response — a metric used to infer efficacy.

Expert after expert at the meeting described how much guesswork is involved in that effort. No one knows which variant of the virus will dominate in the fall, when federal officials consider a new surge highly likely. There is some chance that before then, another variant like Omicron will emerge and redraw the coronavirus picture in a wholly unexpected way. “Not likely, but it’s there,” Dr. Marks said of that possibility.

Trevor Bedford, a biostatistician at the Fred HutchinsonCancer Research Center, said the coronavirus had been mutating at several times the rate of the flu virus, for which vaccines are redesigned annually. While that pace may slow, the virus’s plasticity indicates it “is likely to keep on evolving,” he said.

How exactly it will do that is anyone’s guess. “There’s no guarantee that every emergent variant is going to be the basis for the next variant,” warned Dr. Michael Nelson, an immunologist at the University of Virginia Medical School.

Meanwhile, federal officials and their outside advisers continue to grapple with what the threshold is for determining that existing vaccines are not doing a good enough job. Dr. Marks said the committee’s consensus appeared to be that Covid vaccines should prevent severe disease, not necessarily infection or mild disease.

The question was especially relevant because just last week, the F.D.A. authorized a second booster for Americans 50 and older, along with some others. But the C.D.C. director outright recommended those shots only for people 65 and older, and anyone 50 to 64 with serious underlying health conditions.

Some immunologists and vaccine experts have said the F.D.A. lacked the necessary data to authorize second boosters, while other health officials have maintained that people should have the option of another shot.

Dr. James E.K. Hildreth, the president of Meharry Medical College in Tennessee and a committee member, asked Dr. Marks why he did not solicit the panel’s advice before deciding whether to authorize a second booster.

Dr. Marks said the F.D.A. did not consider offering a second booster to be “a major expansion or a major change.” Jerry Weir, another senior agency official, said the F.D.A. expected to ask the advisory panel to review any reconfiguration of the existing vaccines before moving forward with emergency authorization.

Sharon Alroy-Preis, the director of public health services for Israel’s Health Ministry, told the panel that administering a second booster for those 60 and older earlier this year saved lives. The Israeli presentation seemed to back up the F.D.A.’s decision.

But European Union regulators concluded on Wednesday that it was “too early” to administer second booster shots to the general population, but reasonable to offer them to people 80 and older.

Dr. Amanda Cohn, a senior C.D.C. official, said her agency’s data showed that existing vaccines are more than 80 percent effective in preventing hospitalization in Americans without immune deficiencies — including older people and those with chronic medical conditions. She suggested that Covid treatments after infection may be more effective than additional shots of vaccine in protecting Americans against severe disease.

Dr. Christopher Murray, a professor at the University of Washington whose institute has modeled the pandemic’s trends, predicted that antiviral treatments like the pills recently developed by Pfizer will cut mortality rates even if a new variant as infectious as Omicron and as deadly as Delta emerges.

Dr. John Beigel, a clinical research director at the N.I.H., described his agency’s research comparing how well Moderna’s existing vaccine works against modified versions aimed at the known variants, both alone and in combination.

In the first stage, researchers are hoping to rapidly enroll 600 volunteers who have already been vaccinated and received a booster. Some will be given the existing vaccine. Others will get experimental vaccines targeted to the Omicron variant alone as well as three other variations: Omicron plus the Beta variant, the Delta variant and the prototype virus that emerged first in the pandemic.

In an interview on Tuesday, Dr. Beigel said the existing vaccines may still turn out to be the best. He said he hoped results from his trials may be ready by midsummer, although some federal officials are hoping for earlier.

Deciding on the next step, he told the panel, “is going to be challenging.”