The U.S. Food and Drug Administration (FDA) has initiated an investigation into the safety of two approved antibodies designed to prevent respiratory syncytial virus (RSV) infections in infants. The review focuses on Sanofi and AstraZeneca’s Beyfortus, as well as Merck’s Enflonsia, according to information reported by Reuters.
Senior executives from the involved pharmaceutical companies were notified about the probe last week. However, the FDA has not yet specified what data it will require from these companies or outlined any possible regulatory actions regarding the therapies.
Concerns about the safety of these RSV antibodies reportedly began earlier this year when Tracy Beth Høeg, who was then a senior adviser at the FDA and is now acting director of the Center for Drug Evaluation and Research (CDER), started examining potential complications in children who had received these treatments. Høeg’s inquiry led George Tidmarsh, then head of CDER, to instruct staff to re-examine Enflonsia’s approval from June 2025. Beyfortus was approved in September 2024, prior to both Tidmarsh and Høeg assuming their current roles at the agency.
Andrew Nixon, spokesperson for the Department of Health and Human Services (HHS), told Reuters that he did not indicate what prompted Høeg’s probe. Nixon added that the FDA is “rigorously reviewing the available data,” and stated: “will update product labeling if warranted by the totality of the evidence.”
It remains uncertain whether this investigation will lead to restrictions on access to these antibodies or changes in their approval status or labeling.
This latest review is part of a broader trend within HHS toward increased scrutiny of vaccines and other preventive agents intended for infants and children. Last week, for example, the CDC’s Advisory Committee on Immunization Practices voted 8–3 to delay hepatitis B vaccination until two months after birth for some infants—a change from longstanding recommendations to immunize newborns.
Additionally, Vinay Prasad, who leads the Center for Biologics Evaluation and Research alongside Høeg at CDER, recently sent an internal memo stating 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,” Prasad wrote in his message. Further details supporting this claim have not yet been released; however, according to statements from FDA officials cited by Reuters, more information is expected by year-end.
