Inclusion Criteria:  Male or female who is either: born ≥37 weeks of gestation and is age ≥28 days to ≤36 months, defined at the time of randomization, or born <37 weeks of gestation and is age ≥6 months to ≤36 months defined at the time of randomization Subjects diagnosed with RSV infection Subjects with signs of an acute respiratory illness with onset ≤72 hours (for hospitalized subjects) and ≤48 hours (non hospitalized subjects) before the time of signing the ICF In the Investigator's opinion, the subject's caregiver understands and is able to comply with protocol requirements, instructions, and protocol-stated restrictions, and the subject is likely to complete the study as planned  Exclusion Criteria:  Use of or anticipated need for intensive monitoring and associated medical care Underlying immune deficiency, eg, from confirmed human immunodeficiency virus infection or use of an immunosuppressive medication except immunoglobulin A deficiency Receipt of (within 12 months before Screening) or on a waiting list for a bone marrow, stem cell, or solid organ transplant, or who received radiation or chemotherapy (within 12 months before screening) Receiving chronic oxygen therapy at home before admission Receiving an investigational or approved medication that is intended to prevent or treat RSV infection within 30 days or 5 half-lives (whichever is longer) before the first dose of study drug, and/or is currently enrolled in a clinical trial of such a medication