The FDA has informed Merck, Sanofi and AstraZeneca of the safety investigation into their RSV antibodies, though it remains unclear what regulatory action, if any, will be taken.
The FDA is looking into two approved antibodies used to prevent respiratory syncytial virus infections in babies, continuing its recent inquiry into the safety of pediatric preventative agents.
Specifically, the agency is reviewing the safety of Sanofi and AstraZeneca’s Beyfortus and Merck’s Enflonsia, Reuters reported on Tuesday, citing sources familiar with the matter. Senior executives at these companies were informed last week of the probe, though the regulator has yet to say what specific data it will need from them, nor what potential actions could be taken regarding the therapies.
Questions about the safety of these RSV antibodies arose this past summer, according to Reuters, when Tracy Beth Høeg, an outspoken critic of vaccines, started looking for complications in children who had been given these immunizing therapies. Høeg, a senior adviser at the FDA at the time, was last week named acting director of the Center for Drug Evaluation and Research—the agency’s top office in charge of regulating prescription and over-the-counter therapies, including biologics and generics.
In a statement to Reuters, Andrew Nixon, spokesperson for the Department of Health and Human Services, did not indicate what prompted Høeg’s probe.
Nevertheless, as a result of Høeg’s questioning, George Tidmarsh, who at the time was head of the CDER, asked his staff to take a second look at Enflonsia’s June approval according to internal documents reviewed by Reuters. Beyfortus came before Tidmarsh and Høeg’s tenures at the FDA and was given regulatory clearance in September 2024.
It remains unclear if the FDA is looking to restrict the antibodies’ availability or revisit their approval and label, Reuters reported. The FDA is “rigorously reviewing the available data,” Nixon told the publication, noting that it “will update product labeling if warranted by the totality of the evidence.”
This probe into the RSV antibodies continues the HHS’ recent heightened scrutiny on vaccines and other prophylactic agents meant to protect infants and children against infectious diseases. Last week, for instance, the CDC’s Advisory Committee on Immunization Practices voted 8–3 to delay hepatitis B vaccination to two months after birth in some infants, changing the agency’s own decades-old recommendation to immunize newborns.
A few days earlier, Vinay Prasad, Høeg’s counterpart at the Center for Biologics Evaluation and Research, sent out an internal memo to FDA staff, claiming that 10 children had died “because of” COVID-19 vaccination. “For the first time, the US FDA will acknowledge that COVID-19 vaccines have killed American children,” he wrote. Prasad has not yet released further details to back up that claim, though the FDA said it will do so by the end of December.
