The U.S. Food and Drug Administration has approved a new shot designed to prevent respiratory syncytial virus (RSV) infection in infants during their first RSV season, which typically spans the colder months from fall through spring.
The newly approved shot, called Enflonsia (clesrovimab), is the first RSV preventive treatment that uses a single standard dose for all infants, regardless of their weight. This approach simplifies administration and ensures consistent protection throughout the RSV season. Enflonsia contains pre-formed antibodies that help shield babies from RSV before it has a chance to cause serious illness.
RSV is a common seasonal virus that spreads through coughing, sneezing, direct contact with infected individuals, or contact with contaminated surfaces. While it usually causes cold-like symptoms in most people, it can lead to severe complications in infants especially those under six months old as well as older adults. In infants, RSV can cause bronchiolitis (inflammation of the small airways in the lungs) and pneumonia, sometimes resulting in hospitalization. Preventive strategies, including vaccines and antibody treatments, are key to reducing the risk of severe illness.
Enflonsia is administered as a single 105-milligram injection into the baby’s thigh. It offers rapid and long-lasting protection for approximately five months the typical duration of the RSV season. Babies born during RSV season should receive the injection shortly after birth, while those born before the season begins should be given the shot just ahead of the season’s start.
The FDA’s approval is based on data from two clinical trials. In the first trial, both full-term and preterm newborns who received Enflonsia showed a 60% reduction in severe RSV-related lung infections and an 84% reduction in hospitalizations over five months compared to those who received a placebo. The second trial demonstrated that Enflonsia was just as effective and safe as an older RSV preventive treatment, palivizumab, for babies at higher risk due to conditions such as premature birth or existing heart or lung problems.
Enflonsia was also shown to be safe when administered alongside routine childhood vaccines, providing flexibility in scheduling and integration into existing immunization programs. Its fixed dosing eliminates the need for weight-based calculations, streamlining the process for healthcare providers and ensuring that infants receive consistent protection.
After receiving the injection, infants will be monitored for signs of serious allergic reactions, though such events are rare. The most commonly reported side effects include mild skin rashes and redness or swelling at the injection site.
With its convenient dosing and strong clinical performance, Enflonsia offers a promising new option for protecting babies against the leading cause of infant hospitalizations during the RSV season.
