Study to Learn About a Respiratory Syncytial Virus Vaccine in Children at High Risk of RSV Disease

The study will first enroll immunocompetent, RSV-experienced participants before enrolling immunocompromised participants to allow for safety data review. Both Cohorts 1 (chronic conditions) and 2 (immunocompromising conditions) will be stratified into 2 age strata. Cohort 1a will enroll participants 12 to <18 years of age with chronic medical conditions and Cohort 1b will enroll participants 5 to <12 years of age with chronic medical conditions. Cohort 2a will enroll immunocompromised participants 12 to <18 years of age and Cohort 2b will enroll immunocompromised participants 5 to <12 years of age.

Key Inclusion Criteria:

• Participants' age requirements for each study cohort at enrollment, respectively Cohort 1a (chronic medical conditions) 12 to <18 years of age Cohort 1b (chronic medical conditions) 5 to <12 years of age Cohort 2a (immunocompromising conditions) 12 to <18 years of age Cohort 2b (immunocompromising conditions) 5 to <12 years of age
• Participants depending on the study cohort requirements, will be considered by the investigator to be at high risk of LRTI-RSV based on the following disease characteristics and definitions:

Chronic medical conditions:

• Cystic fibrosis
• Medically treated asthma
• Other chronic respiratory diseases and malformations of the lung
• Trisomy 21 (Down syndrome)
• Neuromuscular disease
• Cerebral palsy
• Hemodynamically significant or symptomatic congenital heart disease
• Sickle cell disease
• Confirmed stable HIV disease defined as documented viral load <50 copies/mL and CD4 count >200 cells/mm3 within 6 months before enrollment, and on stable antiretroviral therapy for at least 6 months

Immunocompromising conditions:

• Immunomodulatory therapy: Is on an active immunosuppressive (including cytotoxic) or immunomodulatory therapy at a stable dose. Patients taking steroids as monotherapy must be on a dose of at least 2 mg/kg/day or 20 mg/day or greater OR
• Primary immune deficiency: Has a diagnosed primary immunodeficiency disease OR
• Cellular therapy: Has received a bone marrow or stem cell transplant at least 6 months (180 days) prior to enrollment with adequate immune reconstitution for immunization in the investigator's opinion or has received chimeric antigen receptor T cell (CAR-T) therapy more than 90 days prior to enrollment OR
• Solid organ transplant: Has received a solid organ transplant at least 3 months prior and with no acute rejection episodes within 90 days prior to enrollment and is on ongoing immunosuppressive therapy OR
• End-stage renal disease: Has end-stage renal disease (ESRD) on hemodialysis (HD)
• Participants' weight must be:

Cohort 1a: ≥30.0 kg at enrollment Cohort 1b: ≥14.5 kg at enrollment Cohort 2a : ≥30 kg at enrollment Cohort 2b: ≥14.5 kg at enrollment

•The participant's parent(s)/legal guardian is capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the ICD and in the protocol. Depending on the age of the participant and according to local requirements, participants will also be asked to provide assent as appropriate (verbal or written)

Key Exclusion Criteria:

• Applicable to Cohort 1 (a and b) participants only: Immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination
• Applicable to Cohort 1 (a and b) participants only: Individuals with a history of autoimmune disease, past or present, requiring therapeutic intervention including, but not limited to, systemic lupus erythematosus. Note: Stable type 1 diabetes and hypothyroidism are permitted
• History of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s)
• Bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection
• Individuals with epilepsy or other seizure disorders that is uncontrolled/unstable, or a history of seizures and/or other neurological complications following vaccination
• History of Guillain-Barré syndrome and/or acute polyneuropathy without an underlying etiology.
• Individuals who are pregnant
• Any medical or psychiatric condition, including any active suicidal ideation in the past year or suicidal behavior in the past 5 years or laboratory abnormality, that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study