The Food and Drug Administration said Thursday it had advised drugmakers to update the Covid vaccines to target the KP.2 strain, a descendant of the highly contagious JN.1 variant that began circulating widely in the U.S. this winter.
The announcement came just over a week after an FDA advisory panel voted unanimously to recommend that the Covid vaccines for the fall be updated to target the JN.1 variant or one of its descendants.
Following the vote, there was a disagreement between panel members and Dr. Peter Marks, the agency’s top vaccine regulator, about which strain the agency should choose. Most panel members expressed a preference for JN.1, while Marks preferred selecting a newer strain, such as KP.2.
"We are paying an incredibly high premium for mRNA vaccines to be able to have the freshest vaccines," Marks said, comparing the shots to buying milk from the store.
Following the committee meeting, the FDA said that on June 6 it initially advised the drugmakers to target the JN.1 variant. However, the agency has continued to monitor the circulating strains, and "based on the most current available data, along with the recent rise in Covid-19 cases in areas of the country, the agency has further determined that the preferred JN.1-lineage" for the updated vaccines is the KP.2 strain, "if feasible," the FDA said.
JN.1 has largely fallen out of circulation in the U.S., according to the Centers for Disease Control and Prevention. As of Saturday, KP.2 accounts for 22.5% of new Covid cases in the U.S. KP.3, a sister variant, accounts for 25% of new cases.
The FDA’s decision will allow drugmakers to begin producing and distributing the shots, which are expected to be used as part of a fall Covid vaccination campaign.
Three drugmakers are producing Covid vaccines: Pfizer, Moderna and Novavax. Pfizer's and Moderna's vaccines are mRNA-based, while Novavax's is protein-based. Because protein-based vaccines take much longer to manufacture, Novavax has indicated it won't be able to make a KP.2 vaccine in time for the fall. Instead, it is expected to distribute a JN.1 vaccine, which it had already been producing.
This is the third time the vaccines have been updated to target the circulating strains. The process of selecting the next round of vaccines is falling into a routine, similar to how the annual flu shot is updated, with vaccine experts selecting the strain in the spring for a vaccination campaign in the fall.
During the advisory committee meeting, the drugmakers presented data showing that a JN.1 vaccine should generate higher levels of antibodies against circulating strains of the virus compared to the current vaccine, which targets XBB.1.5, a subvariant that’s no longer in circulation.
The committee did not make a recommendation on who should get the updated vaccine. That will be left up to the CDC, which is holding its own advisory committee meeting later this month.
