The Food and Drug Administration (FDA) has approved a new immunization to protect infants from respiratory syncytial virus (RSV).
Merck’s clesrovimab (Enflonsia) is a long-acting monoclonal antibody similar to nirsevimab (Beyfortus) from Sanofi and AstraZeneca. The FDA authorized its use in infants born during or entering their first RSV season.
The immunization is given as a single 105 milligram dose regardless of weight. Protection is expected to last for five months.
RSV is the leading cause of hospitalization among U.S. infants. In clinical trials, clesrovimab reduced RSV-associated hospitalizations by 84% through five months compared to a placebo, according to Merck. It reduced medically attended lower respiratory infections by 61%. The most common adverse reactions were redness at the injection site, swelling at the injection site and rash, all of which occurred in less than 4% of infants receiving the immunization.
The Centers for Disease Control and Prevention’s (CDC’s) Advisory Committee on Immunization Practices (ACIP) is scheduled to make recommendations for the use of clesrovimab when it meets June 25-27, although the makeup of the committee is uncertain. Health and Human Services Secretary Robert F. Kennedy Jr. fired all 17 voting members Monday and said he would be replacing them.
If approved, clesrovimab will give providers an option for protecting infants from RSV along with nirsevimab and maternal vaccination with RSVpreF (Abrysvo) from Pfizer, both of which were approved in the fall of 2023.
A study published last month in the CDC’s Morbidity and Mortality Weekly Report found hospitalization for RSV fell by half among babies under 3 months in the 2024-’25 RSV season when these products became widely available compared to 2018-’20.
In April, an ACIP work group said there would be benefits to having multiple products for infants in case RSV develops resistance to one. There also may be fewer supply issues and more competitive pricing, both of which were major concerns when nirsevimab was rolled out in the 2023-’24 season.
Merck said it expects ordering to begin in July with shipments delivered before the 2025-’26 RSV season.
Resources
- Information on prescribing clesrovimab
- AAP RSV resources
- AAP Red Book chapter on RSV
- Information for parents from HealthyChildren.org on RSV symptoms and when to call a doctor
- Information from the CDC on using nirsevimab
- Information from the American College of Obstetricians and Gynecologists on maternal RSV vaccine Abrysvo
