The FDA approved the monoclonal antibody clesrovimab-cfor for the prevention of respiratory syncytial virus lower respiratory tract disease in newborns, Merck announced.
Merck said it plans to make the shot available for the 2025-2026 RSV season under the brand name Enflonsia. “RSV disease is the leading cause of infant hospitalization in the United States and can lead to serious respiratory conditions like bronchiolitis and pneumonia,” Octavio Ramilo, MD, chair of infectious diseases at St. Jude’s Children’s Research Hospital in Memphis, Tennessee, and principal investigator for Merck, said in a press release. “Enflonsia combines dosing convenience with strong clinical data showing significant reductions in RSV disease incidence and hospitalizations, making it a promising new intervention to help protect infants from RSV.”
The approval was based in part on results from a phase 2b/3 trial in which one dose of clesrovimab reduced RSV-associated medically attended lower respiratory infections by 60.5% for 5 months compared with placebo, according to the release. It reduced hospitalizations by 84.3% through 5 months.
Clesrovimab is the second one-shot mAb to be approved for RSV prevention in the U.S.
In 2023, the FDA approved nirsevimab, which the CDC recommends for infants aged younger than 8 months who are born during or entering their first RSV season and are not otherwise protected because their mother was not vaccinated against RSV, has an unknown vaccine status or was vaccinated within 14 days of giving birth. The CDC also recommends nirsevimab for children aged 8 to 19 months who are entering their second RSV season and have certain risk factors for severe disease.
Unlike nirsevimab, which is dosed by weight, clesrovimab has a fixed dose regardless of infant size. Ramilo told Healio last fall that one dose of clesrovimab was sufficient at preventing severe RSV disease in high-risk children, including preterm infants and those with chronic lung disease or congenital heart disease, compared with five doses of palivizumab — an mAb that has wider global availability than nirsevimab.
According to the press release, the most common adverse events associated with clesrovimab were injection-site erythema, injection-site swelling and rash.
The CDC’s Advisory Committee on Immunization Practices is scheduled to vote on recommendations for clesrovimab at its June 25-27 meeting, although it is unclear who will be making the votes after HHS removed all 17 members this week.
