An advisory committee to the Food and Drug Administration on Thursday raised doubts about shifting toward a yearly Covid booster for most adults and children, saying too many questions about the virus still remain unanswered. 

The FDA convened its Vaccine and Related Biology Products Advisory Committee to discuss how the Covid vaccines may change moving forward.

On Monday, the agency published briefing documents proposing annual Covid shots that target the latest variants of the virus — an approach similar to the yearly flu shot.

But during Thursday’s meeting, several members of the committee said they felt apprehensive about making any decisions about when the vaccines are administered, given that the virus is still so new. 

Unlike the flu, which flourishes in the winter months, Covid’s spread has often been erratic, consistently mutating into new variants and failing to settle into a predictable seasonal pattern. A common refrain at the meeting was that Covid was not like the flu.

“We don’t know what’s going to happen,” said Dr. Eric Rubin, editor-in-chief of the New England Journal of Medicine. “It’s hard to say that it is going to be annual at this point.”

The virus may mutate multiple times a year to become more virulent or more immune-evasive — or it may not.

“We may or may not need annual vaccination,” said Dr. Cody Meissner, a pediatrician at Tufts University School of Medicine. “It’s just awfully early, it seems to me, in this process to answer that.”

Other committee members said they worried about the amount of protection people would have against the virus if the U.S. shifted to a yearly vaccination schedule, and whether it would be better to wait for more effective vaccines. 

Thursday’s meeting included a presentation from the National Institutes of Health on the next generation of Covid vaccines that could provide broad protection against both known and unknown strains of the virus — though officials noted that a broadly protective vaccine is likely a long way off.

While the effectiveness of the Covid vaccines from Pfizer-BioNTech and Moderna against severe disease appears to last for months or even years, their protection against infection declines only after a few months.

“We need broader protection,” said Dr. Pamela McInnes, the retired deputy director of the National Center for Advancing Translational Sciences at the National Institutes of Health. “We don’t want to be chasing this virus.”

During Thursday’s meeting, Dr. Peter Marks, the FDA’s top vaccine regulator, acknowledged that simplifying the Covid vaccine schedule to be exactly like the flu may not be possible.

The FDA had proposed that the committee meet each June to select the strain or strains for the yearly vaccine, which would give manufacturers enough time to make enough doses for a fall campaign.

Dr. Jerry Weir, director of the Division of Viral Products at the FDA’s Office of Vaccines Research and Review, said that even if the U.S. adopted a yearly approach, if a new, dangerous variant were to emerge, the agency would still likely convene an emergency meeting to discuss whether new boosters are needed.

Some committee members said they would prefer to make multiple yearly meetings on the Covid vaccines the norm.

Meeting once a year, they said, may give off the impression to the public that Covid is only a threat in the fall and winter months, like the flu — which is not the case.

“I think this pattern is not necessarily the flu,” said Dr. Henry Bernstein, a professor of pediatrics at the Zucker School of Medicine at Hofstra University in New York. “We need to communicate that there is still value in getting vaccines outside the typical influenza window.”

They also questioned whether offering the boosters in the fall would mean that people could not get boosters during any other time of the year, meaning that people had a limited time window to get protected.

While the committee was indecisive about moving forward on annual boosters, they were certain about the need to simplify the formulation for the vaccines.

Currently, the bivalent vaccine, which targets the omicron subvariants BA.4 and BA.5, in addition to the original strain of the virus first identified in Wuhan, China in 2019, is only available as a booster shot. The primary vaccination series, which is given to anyone who is unvaccinated, still only targets the original strain.

In a unanimous vote, the committee recommended using the bivalent formula in all Covid vaccines moving forward, not just for booster shots.

The FDA is not obligated to accept its committee’s recommendation, although it often does.

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