According to multiple reports, the FDA is investigating the safety of a pair of already-approved protective treatments for respiratory syncytial virus.
The FDA is set to launch a new safety review into a pair of approved monoclonal antibodies for respiratory syncytial virus (RSV) after the agency spoke with executives at Merck, Sanofi, and AstraZeneca, according to multiple reports, first published by Reuters.1,2
The preventive therapies the FDA plans to review are
Reuters reported that FDA officials, appointed under US Health and Human Services Secretary Robert F. Kennedy Jr, made inquiries into the RSV preventive therapies in the summer and that senior FDA adviser Tracy Beth Høeg began questioning safety in June.
In August 2023, 2 months after nirsevimab was approved, previous members of the CDC's Advisory Committee on Immunization Practices (ACIP)
Data at the time of approval revealed nirsevimab demonstrated an 82.21% reduction in RSV-related hospitalization in infants younger than 12 months, reported from the phase 3b HARMONIE study. The approval was widely accepted by pediatric health care professionals as a great advancement in preventing RSV-associated lower respiratory tract disease. Since its 2023 approval, nirsevimab has demonstrated continued positive data,
Additionally, according to an NBC News article, a Sanofi spokesperson stated that the safety and efficacy of nirsevimab have been "demonstrated in over 50 clinical studies and real-world studies, involving more than 400,000 infants."
Clesrovimab was approved based on data from the phase 2b/3 CLEVER trial (MK-1654-004; NCT04767373), a randomized, placebo-controlled trial evaluating a single dose of clesrovimab administered to healthy preterm and full-term infants. Data revealed that clesrovimab demonstrated positive outcomes, meeting all prespecified end points that evaluated a single dose in healthy preterm and full-term infants from birth to 1 year. Results were consistent through both the 5-month and 6-month time points. The study enrolled 3632 participants who were randomly assigned 2:1 to receive either a single fixed dose of clesrovimab (105-mg intramuscular injection) or placebo on day 1.5
A reduction in incidence of RSV-associated medically attended lower respiratory infections that required 1 or more indicators of lower respiratory infection or severity compared with placebo through 5 months post dose was 60.5% (95% CI, 44.2%-72.0%; P < .001).
A spokesperson for Merck stated in an email to NBC News, "We met briefly with FDA representatives last week, and we welcome ongoing scientific exchange and dialogue with the FDA and other regulatory or health authorities, their advisory committees, and scientific leaders on Enflonsia, including its safety profile."2
In 2024, even before the FDA approval of clesrovimab, Robert Frenck Jr, MD, professor of pediatrics in the Division of Infectious Diseases and director of vaccine research at Cincinnati Children’s Hospital in Ohio, highlighted the significance of advances in RSV preventive measures.6
"I think that RSV [prevention] with the maternal immunization and then the nirsevimab is really a big deal," Frenck stated. Reflecting on historical parallels, he recalled the substantial reduction in rotavirus-associated hospitalizations following vaccine introduction. "Before that, we used to have kids who were just the whole wards in the hospital. The units in the hospital were full of kids who were having dehydration due to rotavirus-associated diarrhea, and now that's basically gone or significantly decreased with the rotavirus vaccine."
Currently, both nirsevimab and clesrovimab are recommended to prevent severe RSV disease in infants, in addition to Pfizer's maternal RSV vaccine, RSVpreF (Abrysvo).7
NBC News reported it is unclear at this time what the FDA's specific intentions are for the review, though Andrew Nixon, spokesperson for the US Department of Health and Human Services, stated via email to NBC News, "FDA routinely evaluates emerging safety information and will update product labeling if warranted by the totality of the evidence."2
Reports of the safety review into the monoclonal antibodies for RSV come a week after a shake-up in recommendations for the hepatitis B vaccine and its dosing timeline,
The ACIP voted to update its recommendation for the hepatitis B virus vaccine for infants born to women with hepatitis B surface antigen (HBsAg)–negative status. Though there is "no change to the vaccine recommendation for infants born to women who test HBsAg positive or have an unknown HBsAg status; existing recommendation remains the same," the committee voted 8 to 3 to accept the following updated recommendation:
"For infants born to HBs-Ag-negative women: ACIP recommends individual-based decision-making, in consultation with a health care provider, for parents deciding when or if to give the HBV vaccine, including the birth dose. Parents and health care providers should consider vaccine benefits, vaccine risks, and infection risks. For those not receiving the HBV birth dose, it is suggested that the initial dose is administered no earlier than 2 months of age. Y/N"
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