The panel endorsed targeting a variant of the coronavirus that is now receding, though some officials suggested aiming at newer versions of the virus that have emerged in recent weeks.A committee of advisers to the Food and Drug Administration voted on Wednesday to update the formula for the Covid vaccine ahead of an anticipated fall immunization campaign, now an annual step to try to offer better protection against versions of the virus in circulation.The unanimous vote by the 16 advisers recommends a formula aimed at combating the variant JN.1, which dominated infections in the United States in February, or a version of it. In recent weeks, JN.1 has been overtaken by descendants known as KP.2 and KP.3.In the coming weeks, the F.D.A. is expected to formally recommend a variant target for vaccine makers for the next round of shots in the late summer or early fall. Any decision involves some educated guesswork, given that any new vaccine formula won’t be available until months after a variant becomes dominant.“It’s becoming clear that the ideal timing for a vaccine composition decision remains elusive,” said Jerry Weir, an official with the F.D.A.’s vaccine division.Dr. Peter Marks, who oversees that division, urged the committee to consider encouraging the mRNA vaccine makers to focus on the latest versions of the virus in broader circulation.“We always say we shouldn’t be chasing strains, but we’re paying an incredibly high premium for mRNA vaccines to be able to have the freshest vaccines,” he said, referring to the technology used by Moderna and Pfizer. He compared the choice of a vaccine to selecting fresher milk at the grocery store.We are having trouble retrieving the article content.Please enable JavaScript in your browser settings.Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.Thank you for your patience while we verify access.Already a subscriber? Log in.Want all of The Times? Subscribe.