The US Food and Drug Administration has approved a new monoclonal antibody called Enflonsia to help prevent infection with respiratory syncytial virus (RSV), the leading cause of hospitalization in infants. Developed by Merck, the therapy will be given as a single 105-milligram shot to protect newborns and infants from mild, moderate, or severe RSV for up to five months.
According to study materials submitted to the FDA, Enflonsia has shown a similar safety profile to a placebo, with mild adverse reactions such as injection-site swelling and rash in a small number of infants. In mid- to late-stage trials, Enflonsia reduced RSV-associated hospitalizations in infants by over 84% compared to a placebo, while also reducing lower respiratory infections that needed medical attention by more than 60%.
The new antibody joins existing tools such as the FDA-approved RSV antibody Beyfortus and an infant vaccine. However, these therapies have been in short supply during previous seasons, leading to increased hospitalization rates.
Experts say another tool to prevent RSV is long overdue, especially considering the serious complications it can cause in young children. The CDC reports that two to three percent of infants under six months are hospitalized with RSV annually, while up to 80,000 children younger than five are hospitalized due to the virus each year.
Merck aims to make Enflonsia available before the start of the upcoming RSV season, pending approval by the US Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices.
Source: https://edition.cnn.com/2025/06/10/health/rsv-antibody-enflonsia