U.S. regulators are taking a fresh look at infant respiratory syncytial virus (RSV) antibody treatments after concerns raised by vaccine skeptics prompted Robert F. Kennedy Jr.'s health leadership team to initiate new safety inquiries.
The review marks the latest instance in which routine immunization policies are being re-examined under the current administration.
On Friday, the Centers for Disease Control and Prevention's (CDC) Advisory Committee on Immunization Practices (ACIP) voted 8 to 3 to rescind the universal recommendation for a hepatitis B birth-dose vaccine for infants born to hepatitis B surface antigen–negative mothers.
Instead, recommended individual-based decision-making for parents deciding whether to give the hepatitis B vaccine, including the birth dose, to infants born to women who test negative for the virus.
Also Read: Beyfortus Output Tripled As Sanofi, AstraZeneca Scale Up For RSV Season
For those infants not receiving the birth dose, ACIP suggested in its recommendation that the initial dose be administered no earlier than two months of age.
Reuters reported that senior executives at Sanofi SA (NASDAQ:SNY), AstraZeneca Plc (NASDAQ:AZN), and Merck & Co. Inc (NYSE:MRK) were told their approved preventive therapies for respiratory syncytial virus would face additional scrutiny.
The products include Beyfortus, developed by Sanofi and AstraZeneca, and Merck's newer antibody, Enflonsia.
Citing internal documents, Reuters noted that FDA officials appointed under Kennedy began raising questions about the therapies.
CDC's Shift In Vaccine Recommendations
According to Health and Human Services spokesman Andrew Nixon, senior FDA adviser Tracy Beth Hoeg initiated internal safety discussions as early as June. Hoeg previously opposed U.S. COVID-19 policies and has publicly questioned certain childhood vaccines.
The scrutiny intensified after Australian journalist Maryanne Demasi published an August blog post suggesting the therapies might raise seizure risk — a claim contradicted by several safety studies.
In November, George Tidmarsh, then director of the FDA division overseeing RSV products, instructed staff to re-examine the approval of Enflonsia, according to documents reviewed by Reuters. Beyfortus has been available in the U.S. since July 2023.
Hoeg's inquiries led the FDA's Center for Drug Evaluation and Research to hold a call with the drugmakers last week, signaling additional data requests may follow.
The agency did not specify what information it plans to seek. Hoeg has since been named acting director of CDER.
Nixon said the FDA is conducting a comprehensive evidence review and will update product labels if necessary.
Sanofi told Reuters that Beyfortus has demonstrated safety and effectiveness in over 50 studies involving more than 400,000 infants.
Beyfortus Safety
Unlike vaccines, these antibody therapies deliver immediate protection for several months to more than a year.
A CDC analysis found Beyfortus and a maternal RSV vaccine reduced infant hospitalizations by up to 43% during the 2024–25 season.
After Demasi's post, Robert Malone, a Kennedy-appointed member of the national vaccine advisory board, said he regretted recommending widespread use of Enflonsia. At the same June meeting, Hoeg cited an "unfavorable imbalance" in mortality from late-stage trials, though the differences were not statistically significant.
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