The duration of each participant's participation will be 12 months post-dosing/randomization.
The purpose of this study is to determine the efficacy and safety of a single intramuscular (IM) dose of nirsevimab, compared to no intervention, for the prevention of hospitalizations due to lower respiratory tract infection (LRTI) caused by confirmed RSV infection (henceforth referred to as RSV LRTI hospitalizations) in all infants under 12 months of age who are not eligible to receive palivizumab.~The visit frequency will be 1 in-person dosing/randomization visit, with monthly safety follow-up electronic contacts through the first 6 months post dosing/randomization. The study will also include a 12-month (Day 366) final follow-up telephone call.~The study duration will be 12 months post-dosing/randomization.