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FDA advisers recommend updating the coronavirus vaccine to target XBB

The next round of coronavirus shots coming this fall should target the family of XBB variants, a branch of omicron that has become dominant in the United States, vaccine experts told the Food and Drug Administration on Thursday. The FDA will make a final decision in the coming days about the vaccine’s formula.

The unanimous vote from the FDA’s independent advisory panel marks the emergence of global consensus that the vaccine should be rebooted to no longer include the original strain from the early days of the pandemic.

The currently available version of the vaccine is bivalent, meaning it targets both the original strain and the more recent BA.4 and BA.5 omicron variants. But in the four years since the coronavirus began to spread in humans, it has continued to evolve new ways to get around existing immunity.

The newly chosen target, XBB, is a recombinant virus — a mash-up of two descendants of the BA.2 omicron variant. Several flavors of XBB are circulating in the United States today, but the committee and FDA appeared to favor using XBB.1.5, a highly transmissible version of the virus on which vaccine makers have already done significant testing.

Because XBB’s spinoffs are so similar to each other, the hope is that a new shot based off one version will provide a breadth of cross-protection against whichever virus circulates this fall, even if it isn’t an exact match.

“Clearly, the data suggests the old variants are no longer circulating. XBB is. So yes, [a change] makes sense,” said Adam C. Berger, director of the Division of Clinical and Healthcare Research Policy in the Office of Science Policy of the National Institutes of Health.

Leaders of Moderna, Pfizer and Novavax, the vaccine companies that provide shots in the United States, presented data from animal and some limited human testing for various updated candidates. The potential timeline for distributing the shots varies depending on which strain is chosen by the FDA, with companies able to provide XBB.1.5 vaccines earlier than other options.

Updating the vaccine this year was a straightforward decision for committee members. Yet some debated whether the scientific understanding of the virus is settled enough to predict that the shot will be updated annually, similar to how the flu vaccine is updated each year. Viral evolution is inherently unpredictable, and the seasonal pattern of this virus is still emerging.

Calling it the 2023-2024 coronavirus vaccine “suggests this will be once a year, and I’m not sure personally we’re there with this virus — that it’s not necessarily seasonal,” said Henry Bernstein, a professor of pediatrics at the Zucker School of Medicine at Hofstra/Northwell in New York.

Those uncertainties must be balanced against the need for a plan that will allow companies to manufacture sufficient doses, and allow public health officials to clearly communicate when people will need to get their shots, said Peter Marks, director of the Center for Biologics Evaluation and Research at the FDA.

“We all certainly agree that covid-19 is not influenza, but from a public health standpoint in which you need to make tens upon tens of millions of vaccine doses, get them deployed and get them into people’s arms … it reduces to a similar type of campaign,” Marks said.

A big concern may turn out to be uptake of the vaccine. Only 1 in 5 adults has received a bivalent booster, according to data from the Centers for Disease Control and Prevention.

That worries public health experts because while immunity from vaccinations and infections continues to protect most people from severe illness and death, protection clearly wanes over time. Data presented at the meeting showed that protection against hospitalization drops considerably four to six months after a bivalent booster. Older adults are most vulnerable.

“Barring some exceptional development of a resistant virus … I think we have one chance this fall to get vaccines into arms,” Marks said.

Scientists are working on an array of next-generation vaccines that could be more variant-proof, longer-lasting or able to shut down transmission of illness. But in the near term, the most practical option is to track the virus and to keep updating the vaccine as it evolves — an uncertain chase that several committee members said was unsatisfying, if necessary.

“We have to be prepared that this is going to be a continuous process,” said Jerry Weir, director of the Division of Viral Products within the FDA’s Center for Biologics Evaluation and Research.

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