Researchers recently performed a multi-site study both inside and outside the United States to determine the efficacy of a monoclonal antibody against respiratory syncytial virus (RSV) in preventing medically attended lower respiratory infection and hospitalization in healthy infants (Zar HJ, et al. Clesrovimab for Prevention of RSV Disease in Healthy Infants. N Engl J Med. 2025 Oct 2;393(13):1292-1303).
RSV causes an estimated 12.9 million lower respiratory tract infections and 2.2 million hospitalizations worldwide. Most hospitalizations occur in healthy children during the first six months of life. Currently, a monoclonal antibody against RSV (nirsevimab) and maternal bivalent prefusion F vaccine (ABRYSVO) are available to prevent this disease. Clesrovimab is, like nirsevimab, a monoclonal antibody directed against the RSV fusion protein. However, unlike nirsevimab, it is directed against a site on the fusion protein that recognizes both prefusion and postfusion conformations. The site recognized by clesrovimab is highly conserved, which reduces the possibility of viral escape.
A total of 3,614 infants received an injection: 2,412 received a 105-milligram dose of clesrovimab and 1,202 received placebo. Subjects were followed for 150 days. Clesrovimab was 60.4% effective at preventing medically attended lower respiratory tract infections and 84.2% effective at preventing hospitalizations. Serious adverse events were the same in the clesrovimab and placebo groups.
On June 9, 2025, the FDA licensed clesrovimab to be administered as a single-dose, intramuscular injection up to 8 months of age before or during the infant’s first RSV season.
Contributed by: Paul A. Offit, MD
Researchers recently performed a multi-site study both inside and outside the United States to determine the efficacy of a monoclonal antibody against respiratory syncytial virus (RSV) in preventing medically attended lower respiratory infection and hospitalization in healthy infants (Zar HJ, et al. Clesrovimab for Prevention of RSV Disease in Healthy Infants. N Engl J Med. 2025 Oct 2;393(13):1292-1303).
RSV causes an estimated 12.9 million lower respiratory tract infections and 2.2 million hospitalizations worldwide. Most hospitalizations occur in healthy children during the first six months of life. Currently, a monoclonal antibody against RSV (nirsevimab) and maternal bivalent prefusion F vaccine (ABRYSVO) are available to prevent this disease. Clesrovimab is, like nirsevimab, a monoclonal antibody directed against the RSV fusion protein. However, unlike nirsevimab, it is directed against a site on the fusion protein that recognizes both prefusion and postfusion conformations. The site recognized by clesrovimab is highly conserved, which reduces the possibility of viral escape.
A total of 3,614 infants received an injection: 2,412 received a 105-milligram dose of clesrovimab and 1,202 received placebo. Subjects were followed for 150 days. Clesrovimab was 60.4% effective at preventing medically attended lower respiratory tract infections and 84.2% effective at preventing hospitalizations. Serious adverse events were the same in the clesrovimab and placebo groups.
On June 9, 2025, the FDA licensed clesrovimab to be administered as a single-dose, intramuscular injection up to 8 months of age before or during the infant’s first RSV season.
Contributed by: Paul A. Offit, MD