Evaluate the Safety and Efficacy of Nirsevimab in Healthy Preterm and Term Infants in China

This is a Phase 3 randomized, double-blind, placebo-controlled, single-dose study to determine if nirsevimab will prevent medically attended RSV-confirmed LRTI in healthy preterm and term infants entering their first RSV season. The population to be enrolled is healthy preterm and term infants \> 29 weeks 0 days GA entering their first RSV season, who would not receive RSV prophylaxis based on the American Academy of Pediatrics (AAP) or other local or national guidelines. Approximately 800 subjects will be randomized 2:1 to receive a single IM dose of nirsevimab 50 mg (if weight \< 5 kg) or 100 mg (if weight ≥ 5 kg) (N = 530) or placebo (N = 270). Randomization will be stratified by subject age at the time of randomization (≤ 3 months, \> 3 to ≤ 6 months, \> 6 months), and by GA (\< 35 weeks GA, ≥ 35 weeks GA). Enrollment of infants \> 6 months of age will be limited to approximately 100. All subjects will be followed through 1 year after dose administration. An independent data monitoring committee will review safety data regularly and make recommendations regarding further study conduct. Around 40 investigational study centres participate in the study.