The EMBRACE Study: Enflonsia Monoclonal in Babies - RSV Antibody Concentration Evaluation

Inclusion Criteria: 1. An infant who is \<8 months of age at the time of immunization and born during or entering their first respiratory season. 2. The infant is in good health as established by medical history and investigator's discretion before entering the study. Chronic medical conditions are acceptable, provided that they are stable. 3. Written informed consent is obtained from the participant's parent(s)/legally authorized representative(s) (LAR) prior to performing any study specific procedures, including screening evaluations. 4. At least one parent/legally authorized representative of the subject is willing and able to maintain communication with the study site for the duration of the study. 5. Subject's parent(s)/legally authorized representative(s) is able to understand and comply with the requirements of the protocol including follow-up and illness visits as judged by the investigator. 6. Subject is available to complete the follow-up period, which will be approximately 6 months after receipt of the dose of study drug. Exclusion Criteria: 1. Any fever (≥ 100.4°F \[≥ 38.0°C\], regardless of route) or acute illness within 3 days prior to enrollment. 2. Any current or expected receipt of immunosuppressive agents including systemic steroids (except for the use of topical steroids according to the judgment of the investigator). 3. Known immunodeficiency, including human immunodeficiency virus (HIV). 4. Any known allergy or hypersensitivity to immunoglobulin products. 5. Hypersensitivity, anaphylaxis, or seizures within 72 hours after any previous administration of a vaccine. 6. Receipt of polyclonal antibodies and/or plasma at any time prior to or planned during the study follow-up period. 7. Receipt of palivizumab, nirsevimab, or other RSV monoclonal antibody or any RSV vaccine at any time prior to or planned during the study. 8. Maternal receipt of an RSV vaccine during her pregnancy with the infant participant. 9. Use of any investigational product or non-registered product (drug or vaccine) other than the study product during the period starting 30 days before study product administration, or planned use during the study period. 10. Concurrent enrollment in another interventional study. 11. Any other condition that, in the judgment of the investigator, would be a risk to subject's safety and/or may interfere with study procedures or interpretation of results. 12. Unable to obtain baseline blood (minimum 0.5 mL) or nasal sample.