Study on a Live-attenuated Respiratory Syncytial Virus Vaccine for Assessment of Safety, Transmissibility, and Genetic Stability of the Vaccine Virus Among Close Contacts in Infants and Toddlers 6 to < 24 Months of Age in Puerto Rico (USA)

Inclusion Criteria: * Aged 6 months to \< 24 months on the day of inclusion (from the day of the 6 months after birth to the day before the 2nd birthday) * Participants who are healthy as determined by medical evaluation including medical history. * Born at full term of pregnancy (≥ 37 weeks) or born after a gestation period of 27 through 36 weeks and medically stable as assessed by the investigator, based on the following definition: "Medically stable" refers to the condition of premature infants who do not require significant medical support or ongoing management for debilitating disease and who have demonstrated a clinical course of sustained recovery by the time they receive the first dose of study intervention * Attends a daycare facility at least 3 days per week and 4 hours per day at which the participant would be in a contact group/playroom of at least one other child 6 to \< 24 months of age who will participate in this study or is a member of a household, which includes at least one other child 6 to \< 24 months of age who will participate in this study Exclusion Criteria: * Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive therapy, such as anti-cancer chemotherapy or radiation therapy, within the preceding 6 months; or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3 months) * Known systemic hypersensitivity to any of the study intervention components…