Efficacy, Immunogenicity, and Safety Study of a Respiratory Syncytial Virus Vaccine in Infants and Toddlers

Inclusion Criteria: -Aged 6 months to < 22 months on the day of inclusion (means the day of the 6-month birthday to the day before the 22-month birthday)

• Participants who are healthy as determined by medical evaluation including medicalhistory

• Born at full term of pregnancy (≥ 37 weeks)

Exclusion Criteria: Participants are excluded from the study if any of the following criteria apply:

• Known or suspected congenital or acquired immunodeficiency; or receipt ofimmunosuppressive 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 3months)

• Known systemic hypersensitivity to any of the study intervention components, orhistory of a life-threatening reaction to the study intervention used in the studyor to a product containing any of the same substances

• Chronic illness that, in the opinion of the investigator, is at a stage where itmight interfere with study conduct or completion

• History of medically diagnosed wheezing

• Any acute febrile illness in the past 48 hours that according to investigatorjudgment is significant enough to interfere with successful inoculation on the dayof vaccination. A prospective participant should not be included in the study untilthe condition has resolved or the febrile event has subsided.

• Probable or confirmed ongoing case of viral respiratory infection (includingCOVID-19, influenza, rhinovirus, etc.) at the time of enrollment. A prospectiveparticipant should not be included in the study until the respiratory infection hasresolved.

• Member of a household that contains an immunocompromised individual, including, butnot limited to:

• a person who is HIV infected

• a person who has received chemotherapy within the 12 months prior to studyenrollment

• a person who has received (within the past 6 months) or is receiving (at thetime of enrollment) immunosuppressant agents

• a person living with a solid organ or bone marrow transplant

• Potential close contact with other immunocompromised individual within 30 days aftereach vaccination as per investigator's discretion

• Participant's biological mother's previous receipt or planned administration of aninvestigational RSV vaccine during pregnancy and/or breastfeeding.

• Receipt or planned receipt of any of the following vaccines prior to enrollment orafter the first study intervention administration:

• Any other intranasal live attenuated vaccine within the 28 days prior to andafter Dose 1 study administration

• Unless given on the day of Dose 1 study administration, any other injectablelive attenuated vaccines within the 28 days prior to and after. Concomitantreceipt on the day of Dose 1 study administration is allowed.

• Previous receipt of an investigational RSV vaccine or receiving any anti-RSV product (such as ribavirin or RSV immune globulin) at the time of enrollment. Previousreceipt of an RSV monoclonal antibody within 6 months prior to the first studyvaccine administration.

• Receipt of immune globulins, blood or blood-derived products in the past 3 months

• Receipt of intranasal and intra-ocular medications within 3 days prior to studyenrollment

• Participation at the time of study enrollment or planned participation during thepresent study period in another clinical study investigating a vaccine, drug,medical device, or medical procedure The above information is not intended tocontain all considerations relevant to a patient's potential participation in aclinical trial.