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An FDA advisory committee voted unanimously, 16-0, Wednesday to recommend that the COVID-19 vaccines for the 2024-2025 season target the JN.1 strain of the virus.

"From my review of the data, it appeared that the newer variants that are appearing -- KP.2, KP.3, and maybe some others that are coming up -- the potential for immunogenicity from a JN.1 vaccine to cover those variants seems to be pretty good," said Archana Chatterjee, MD, PhD, of Rosalind Franklin University of Medicine and Science in Chicago. "Antigenically they are close, and from the experience we had with [the] XBB [strain], it appears even with some variation, there's still reasonably good protection. So from that perspective, I would say that JN.1 is a reasonable strain to include."

Melinda Wharton, MD, MPH, of CDC's National Center for Immunization and Respiratory Diseases, agreed. "We can't predict which variants are going to emerge over the coming months," she said. "It may very well not be any of the ones that we're talking about today, but they're likely to be related to JN.1. So having a vaccine that's the trunk of the tree rather than the branches makes sense to me."

Chatterjee and Wharton were speaking during a meeting of the FDA's , where members were asked to specifically vote on whether they recommend a monovalent JN.1-lineage vaccine for the 2024-2025 formula. They were also asked to discuss considerations for the selection of a specific JN.1 lineage strain -- such as JN.1 or KP.2 -- for COVID-19 vaccines to be used in the U.S.

During the meeting, the committee heard presentations from representatives of three COVID-19 vaccine manufacturers: Moderna, Pfizer, and Novavax. Both Moderna and Pfizer representatives said they each had two mRNA vaccines in process -- one targeting the JN.1 variant and the other targeting the KP.2 variant. The Moderna spokesman said his company's vaccines would be ready for shipping in August, while the Pfizer representative said his firm's vaccines would be ready for shipping "immediately upon approval." All three company representatives said that their vaccines also were found to provide good coverage for other closely related subvariants.

The Novavax representative said his company had developed a single vaccine, for JN.1, on a protein-based platform, and that it would be ready for shipping in August. Several committee members said part of the reason they voted in favor of the JN.1 strain was to make sure that Novavax's vaccine was included so that patients could have a choice of vaccine type.

"Unless we have a compelling reason to do otherwise, given the limitations of Novavax, I think we do need to just recommend the JN.1 version," said Mark Sawyer, MD, professor of clinical pediatrics in the division of infectious diseases at the University of California San Diego. "Otherwise there are going to be equity issues or access issues to those who are reluctant to get an mRNA vaccine."

Adam Berger, PhD, division director of clinical and healthcare research policy at the NIH, said that although he agreed with recommending the JN.1 vaccine, he was uneasy about having any obligation to always include a protein-based option. "I'm concerned that it could end up putting us in a position in the future where, depending on what protein vaccines can be made from or made out of, that that will require us to go down this path," he said. "I'd like to make sure we don't get in that position in the future ... I think JN.1 is the right call, so that doesn't seem to be an issue, but I just want to point that out -- that could present some type of problem for us at some point."

The committee also heard from David Wentworth, PhD, chair of the WHO's Technical Advisory Group on COVID-19 Vaccine Composition, who reviewed his group's recommendation at its April meeting that future formulations of COVID-19 vaccines should aim to induce enhanced neutralizing antibody responses to JN.1 and its descendent lineages. That could include a monovalent JN.1 vaccine, although other formulations could be considered, he said.

An released in advance of the meeting noted that "in prior years there appears to have been an inverse relationship between the time since vaccination and vaccine effectiveness, such that COVID-19 vaccine effectiveness against SARS-CoV-2 sublineages appears to wane over time and that better matching of the vaccine to circulating strains is associated with improved neutralizing antibody titers."

"Consistent with this observation, a decrease in effectiveness of COVID-19 vaccines (2023-2024 Formula) against COVID-19 caused by JN.1 lineage viruses has been reported," the authors wrote. "Available data suggest that updating the current formula of COVID-19 vaccines to more closely match currently circulating JN.1 lineage viruses is warranted for the anticipated 2024-2025 respiratory virus season in the U.S."

FDA officials will take the advisory panel's recommendation into account when it considers which updated vaccines to approve and/or authorize. The agency does not have to follow its advisory panels' recommendations, but often does. The CDC's Advisory Committee on Immunization Practices (ACIP) will also weigh in with recommendations on use of the vaccines.

The FDA advisory committee meeting comes at a time when vaccine uptake is low. As of May 11 -- the latest date for which figures were available -- 22.5% of adults reported receiving an updated COVID vaccine since mid-September 2023, and 14.4% of children ages 6 months to 17 years were reportedly up to date on their COVID shots, .

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