Nirsevimab Demonstrates Durable Efficacy in Preventing RSV-Related Hospitalizations in Children
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Reviewed by Dat Tien Nguyen, B.A, ScM.
Translated by Nhi Phuong Quynh Le, B.A |
Posted on June 16th, 2025
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Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infections in infants. Nirsevimab, a monoclonal antibody that targets the RSV F protein to block viral fusion, has previously shown promise in preventing infection. A recent study funded by AstraZeneca and Sanofi has now reported on the long-term protective effects of nirsevimab.
This phase 3 clinical trial was carried out in Germany, France, and the United Kingdom, enrolling 8,057 infants with a median age of 4 months. About 14% of the participants were born preterm, and nearly two-thirds weighed more than 5 kilograms at baseline. Infants were randomly assigned to receive either a single intramuscular dose of nirsevimab or standard care. The dosage of nirsevimab was weight-adjusted: 50 mg for infants under 5 kg, and 100 mg for those 5 kg and above. Notably, the control group did not receive a placebo.
After six months of follow-up, nirsevimab was shown to reduce the risk of RSV-related hospitalization by 82.7%. Subgroup analyses indicated that the protective effect was strongest in infants under 3 months of age and that nirsevimab was equally effective whether administered before or during the RSV season. The sustained protection is likely due to its extended half-life of approximately 70 days, significantly longer than that of naturally acquired maternal antibodies (about 50 days).
This phase 3 clinical trial was carried out in Germany, France, and the United Kingdom, enrolling 8,057 infants with a median age of 4 months. About 14% of the participants were born preterm, and nearly two-thirds weighed more than 5 kilograms at baseline. Infants were randomly assigned to receive either a single intramuscular dose of nirsevimab or standard care. The dosage of nirsevimab was weight-adjusted: 50 mg for infants under 5 kg, and 100 mg for those 5 kg and above. Notably, the control group did not receive a placebo.
After six months of follow-up, nirsevimab was shown to reduce the risk of RSV-related hospitalization by 82.7%. Subgroup analyses indicated that the protective effect was strongest in infants under 3 months of age and that nirsevimab was equally effective whether administered before or during the RSV season. The sustained protection is likely due to its extended half-life of approximately 70 days, significantly longer than that of naturally acquired maternal antibodies (about 50 days).