Nirsevimab Provides Extended Protection Against RSV-Associated Hospitalization in Infants
|
Reviewed & Translated by Dat Tien Nguyen, B.A, ScM.
|
Posted on September 15th, 2025
|
Nirsevimab is a monoclonal antibody that targets the F protein used by respiratory syncytial virus (RSV) to enter host cells. Earlier studies demonstrated its effectiveness in preventing hospitalization among children, but with a half-life of 71 days, it remained unclear whether protection would extend across the typical four-month RSV season. To address this question, Sanofi and AstraZeneca sponsored a study evaluating the long-term protective effect of nirsevimab.
The phase 3 clinical trial enrolled 8,057 infants with a median age of 4 months. Approximately half were born during the RSV season, 15% were preterm (<37 weeks’ gestation), and 38% had a birth weight under 5 kg. Participants were randomized to receive a single intramuscular injection of either placebo or nirsevimab, dosed at 50 mg for infants weighing under 5 kg and 100 mg for those above.
At the six-month follow-up, nirsevimab significantly reduced the risk of hospitalization from RSV-associated lower respiratory tract infection. The results suggest that the antibody’s extended duration of action may offer greater flexibility for implementation during the RSV season. However, further research is needed to confirm its effectiveness across multiple RSV seasons and diverse epidemiological settings.
The phase 3 clinical trial enrolled 8,057 infants with a median age of 4 months. Approximately half were born during the RSV season, 15% were preterm (<37 weeks’ gestation), and 38% had a birth weight under 5 kg. Participants were randomized to receive a single intramuscular injection of either placebo or nirsevimab, dosed at 50 mg for infants weighing under 5 kg and 100 mg for those above.
At the six-month follow-up, nirsevimab significantly reduced the risk of hospitalization from RSV-associated lower respiratory tract infection. The results suggest that the antibody’s extended duration of action may offer greater flexibility for implementation during the RSV season. However, further research is needed to confirm its effectiveness across multiple RSV seasons and diverse epidemiological settings.