Co-administration Study of an Investigational Live-Attenuated Respiratory Syncytial Virus Vaccine in Infants and Toddlers

This study is a Phase III, randomized, single-blind, placebo-controlled, multi-center study to be conducted in healthy infants and toddlers which will be enrolled at approximately 6 months of age (Cohort 1) and approximately 12 months of age (Cohort 2). The primary objective of the study will be to assess non-inferiority of the RSV infant and toddler (RSVt) vaccine antibody response when administered concomitantly with routine pediatric vaccines at 6 months of age (Diphtheria and Tetanus Toxoids and Acellular Pertussis, Inactivated Poliovirus, Haemophilus b Conjugate and Hepatitis B Vaccine \[Vaxelis® or Pentacel® and Recombivax HB®\] Prevnar 20®, and RotaTeq®), and 12 months of age (M-M-R II, VARIVAX, and Prevnar 20 or per local country recommendations) compared to when administered non-concomitantly.

The study duration is approximately 9 months for each participant.

* Cohort 1: Visits at 6, 7, and 8 and 9 months of age for both groups with visit at 10 months of age for Group 2 only
* Cohort 2: Visits at 12, 13, 14 and 15 months of age for both groups with visit at 16 months of age for Group 4 only
* Routine pediatric vaccines (authorized auxiliary medicinal products (AxMP) will be administered at 6 months in Cohort 1 and 12 months of age in Cohort 2, as per Advisory Committee on Immunization Practice (ACIP) or local country recommendations.

Eligibility Criteria:
Inclusion Criteria:

* Aged 6 months for Cohort 1 and 12 months for Cohort 2 on the day of inclusion ("6 months" means from the day of the 6-month birthday to the day before the 7-month birthday and "12 months" means from the day of the 12-month birthday to the day before the 13-month birthday)
* Participants who are healthy as determined by medical evaluation including medical history and physical examination
* For Cohort 1: Infant received doses of vaccines containing hepatitis B, diphtheria, tetanus, pertussis, Haemophilus influenzae type B (Hib), and inactivated poliovirus vaccine (IPV) antigens, with Advisory Committee on Immunization Practice (ACIP) recommended vaccines. The last dose(s) of these vaccines must be at least 28 days before the first study visit
* Infant received the recommended doses of a recommended pneumococcal conjugate vaccine (as per local schedule) at least 28 days before the first study visit.

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 previous infection with diphtheria, tetanus, Hib, measles, mumps, rubella, rotavirus, pneumococcus, polio, hepatitis B virus
* Known systemic hypersensitivity to any of the study intervention components, or history of a life-threatening reaction to the study intervention used in the study or to a product containing any of the same substances
* Chronic illness that, in the opinion of the investigator, is at a stage where it might interfere with study conduct or completion
* History of medically diagnosed wheezing
* Any acute febrile illness in the past 48 hours that according to investigator judgment is significant enough to interfere with successful inoculation on the day of vaccination. A prospective participant should not be included in the study until the condition has resolved or the febrile event has subsided.
* Probable or confirmed ongoing case of viral respiratory infection (including COVID 19, influenza, rhinovirus, etc.) at the time of enrollment. A prospective participant should not be included in the study until the respiratory infection has resolved.
* Member of a household that contains an immunocompromised individual, including, but not limited to:
* A person living with human immunodeficiency virus (HIV)
* A person who has received chemotherapy within the 12 months prior to study enrollment
* A person who has received (within the past 6 months) or is receiving (at the time 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 after each vaccination as per investigator's discretion
* History of definitive contraindications to any of the concomitant vaccines that will be administered as part of the study protocol
* Participant's biological mother with previous receipt or planned administration of an investigational RSV vaccine during pregnancy and/or breastfeeding
* Receipt of any vaccine in the 4 weeks preceding RSVt vaccine administration or planned receipt of any vaccine outside of study protocol in the 4 weeks following RSVt vaccine administration, except for influenza and/or COVID-19 vaccination, which may be received at least 1 week before or 1 week after RSVt vaccine administration
* 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
* 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 study enrollment
* Previous receipt of an RSV monoclonal antibody within 6 months prior to the first study vaccine administration or planned receipt for duration of the study
* For Cohort 1: Prior receipt of routine 6-month pediatric vaccine doses (as per local schedule)
* For Cohort 2: Prior receipt of routine 12-month pediatric vaccine doses (as per local schedule)
* Participation at the time of study enrollment (or in the 6 weeks preceding the first study intervention administration) or planned participation during the present study period in another clinical study investigating a vaccine, drug, medical device, or medical procedure

Note: The above information is not intended to contain all considerations relevant to a potential participation in a clinical trial.