A Study to Learn About the Safety and Immune Activity of RSVpreF in Children 2 to <18 Years of Age

Inclusion criteria

• Participants 2 to <18 years of age at enrollment
• Participants 2 to <18 years of age should either be healthy or be considered by the investigator to be at high risk of RSV disease based on the presence of 1 of the following chronic medical conditions:

• Cystic fibrosis
• Medically treated asthma
• Other chronic respiratory diseases and malformations of the lung
• Down syndrome
• Neuromuscular disease
• Cerebral palsy
• Hemodynamically significant or symptomatic congenital heart disease
• All participants 2 to <5 years of age must be seropositive for RSV as confirmed by serology.
• Participants' parent(s)/legal guardian(s) and participants, as age appropriate, who are willing and able to comply with all scheduled visits, investigational plan, laboratory tests, and other study procedures, including collection of nasal swabs by participants' parent(s)/legal guardian(s) and by study staff when indicated.
• The participant's parent(s)/legal guardian is capable of giving signed informed consent as described 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).

Exclusion criteria

• Immunocompromised individuals associated with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination.
• Individuals with a history of autoimmune disease or an active autoimmune disease requiring therapeutic intervention, including but not limited to systemic lupus erythematosus. Note: Stable type 1 diabetes and hypothyroidism are permitted.
• Other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.
• 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 a history of epilepsy or other seizure disorders, or a history of seizures and/or other neurological complications following vaccination.
• Previous vaccination with any licensed or investigational RSV vaccine or planned receipt during study participation. Children who may have been exposed to investigational RSV vaccines through maternal immunization will be permitted.
• Receipt of investigational or approved monoclonal antibodies against RSV within 6 months before study intervention administration, or planned receipt throughout the study.
• Receipt of blood/plasma products or immunoglobulins within 28 days before study intervention administration, or planned receipt throughout the study.
• Receipt of chronic systemic treatment with known immunosuppressant medications (including cytotoxic agents or systemic corticosteroids), or radiotherapy, within 60 days before study intervention administration, or planned receipt throughout the study.

Note: Systemic corticosteroids are defined as those administered for ≥14 days at a dose of ≥20 mg/day of prednisone or equivalent (eg, for cancer or an autoimmune disease). Inhaled/nebulized, intra-articular, intrabursal, or topical (skin, eyes, or ears) corticosteroids are permitted.

• Participation in other studies involving study intervention within 28 days prior to study entry and/or for the duration of study participation.
• Investigator site staff directly involved in the conduct of the study and their family members, site staff otherwise supervised by the investigator, and sponsor and sponsor delegate employees directly involved in the conduct of the study and their family members.