Although Covid cases remain low in the U.S., vaccine experts are already looking toward the winter, with eyes on preventing a seasonal surge.
A Food and Drug Administration advisory panel on Wednesday unanimously recommended that the Covid vaccines for the fall be updated to target the highly contagious JN.1 variant or one of its descendants.
JN.1 emerged in the U.S. in late August and by January became the dominant strain in circulation.
Various offshoots of JN.1 soon followed, including the so-called FLiRT variants, KP.1.1 and KP.2. In mid-May, KP.2 overtook JN.1 as the dominant strain in the U.S., and it now accounts for over 1 in 4 new cases, according to the Centers for Disease Control and Prevention.
Natalie Thornburg, a research microbiologist at the CDC, said at Wednesday’s meeting that the coronavirus appears to be adopting a consistent pattern: a dominant “parent” strain takes hold in early winter, and by spring, a handful of descendants emerge. That’s also what happened with the XBB strain last year, she said, which dominated in the winter but gave rise to offshoots in the spring.
The panel’s recommendation didn’t specify whether to include the “parent” JN.1 strain or one of its descendants, but most panel members expressed a preference for JN.1.
"The trunk of the tree is probably our best bet for now," said panel member Dr. Bruce Gellin, the chief of global public health strategy at the Rockefeller Foundation, in a discussion following the vote.
Dr. Peter Marks, the FDA's top vaccine regulator, urged the committee to consider one of the more recent strains, such as KP.2.
“We are paying an incredibly high premium for mRNA vaccines to be able to have the freshest vaccines,” Marks said, a reference to the speed with which new mRNA-based vaccine shots can be developed and produced.
"Will we regret not having been a little bit closer?" he added.
The FDA is expected to make a final decision soon on which strain it will advise drugmakers to target. That will kickstart production of the updated shots, which will be distributed as part of a fall vaccination campaign.
Pfizer said Wednesday it can have updated Covid shots available “immediately upon approval” from the FDA; Moderna said it can have shots available to distribute as early as mid-August.
Novavax said it’s on track to have an updated vaccine that targets JN.1 available in August. However, should the FDA select a different strain, the company said it will not have an updated shot for that specific strain available for the fall vaccination campaign. Novavax uses a protein-based vaccine, which takes longer to manufacture than the mRNA-based vaccines made by Pfizer and Moderna.
All three drugmakers presented data Wednesday showing that a JN.1 vaccine should generate higher levels of antibodies against circulating strains of the virus compared to the current vaccine, which is targeted against XBB.1.5, a subvariant that’s no longer in circulation. Once the updated vaccine is available, the older vaccine will be discontinued.
Covid hospitalizations remain at their lowest levels since the start of the pandemic in 2020, though there are some indications that cases may be starting to creep upward.
CDC data shows that, as of May 25, the weekly test positivity rate was 4.2%, up from 3.4% the week prior. In comparison, in early 2022, when the omicron variant began to rapidly spread, the weekly test positivity rate was around 30%. Thornburg said that virtually all Americans have developed some form of immunity to Covid, either through infection, vaccination or a combination of both.
“We’re sitting at about just below 100% seroprevalence,” she said, referring to the number of people in a population who have been exposed to a virus.
Later this month, a CDC advisory group will make recommendations for who should get the vaccine in the fall.
