NASHVILLE — The Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee on Thursday recommended updating the fall 2024 Covid-19 vaccines to target the XFG variant, nicknamed “stratus.” The vote was nearly unanimous, with all committee members supporting the recommendation and only one abstaining.

The recommendation is intended to guide vaccine manufacturers in formulating doses for the upcoming fall and winter respiratory virus season, when infections typically rise. The committee’s advice is not final; the FDA is expected to issue a formal decision soon, allowing companies to begin production. However, it remains unclear who will formally approve the updated shots, as the agency currently lacks both a permanent commissioner and a dedicated vaccine chief. Following Commissioner Marty Makary’s recent resignation, Kyle Diamantas, the agency’s top food regulator, was named acting commissioner. Thursday’s meeting had been scheduled before Makary stepped down, and his departure played no role in the proceedings.

XFG is a hybrid of two omicron variants and carries mutations that may help it partially evade antibodies, according to Natalie Thornburg, director of the CDC’s respiratory division. As of May 8, XFG and its descendants accounted for more than half of new U.S. infections, with the subvariant XFG.1.1 currently dominant, representing about one in four cases. Despite its prevalence, “XFG and its descendants do not appear to cause more severe illness than earlier strains, although researchers are still studying whether the variants spread more easily,” said William Schaffner, an infectious disease expert at Vanderbilt University Medical Center.

“They also appear to cause similar symptoms to earlier strains, including sore throat, cough, headache, body aches, fever and chills,” Schaffner said. CDC data presented at the meeting showed that Covid was generally less severe last season, with hospitalizations falling below levels seen in the prior three years. The highest hospitalization rates were among infants under 6 months and adults over 65. WastewaterSCAN data indicate that current U.S. Covid activity is at a “medium” level.

During the meeting, Moderna and Novavax presented mouse data suggesting that XFG-targeted vaccines generated higher antibody levels against circulating strains than the current LP.8.1 formulation used by Pfizer and Moderna. Pfizer, however, reported that its XFG vaccine produced antibody levels similar to the current shot. Hana El Sahly, a professor of molecular virology and microbiology at Baylor College of Medicine, noted, “Data on the effectiveness of an XFG vaccine showed it wasn’t overwhelmingly better than the current formulations.” The World Health Organization earlier this month recommended targeting either LP.8.1 or closely related variants like XFG.