The Phase 3 study will be a randomized, double-blind, placebo-controlled trial.

A total of 28,860 infants aged under 12 months, with no history of RSV LRTI hospitalization, will be enrolled in the study.

Participants will be randomly assigned to receive either a single IM dose of nirsevimab or a placebo.

The primary outcome measure will be the rate of RSV LRTI hospitalizations in the two groups.

Secondary outcomes will include incidence of very severe RSV LRTI through the RSV season, the rate of RSV infection, the rate of serious adverse events, and the rate of adverse events related to the study drug.

The duration of the study will be one RSV season, and the study population will be followed for a period of 12 months.