A Study to Assess Safety, Pharmacokinetics Anti-Drug Antibody and Anti-RSV Antibody After 2 Doses of Nirsevimab

Inclusion Criteria:

1. Written informed consent and any locally required authorization obtained from theparticipant's parent(s)/legally authorized representative(s) before performing anyprotocol-related procedures, including screening evaluations

2. Japanese infants of ≤12 months of age eligible to receive palivizumab in accordancewith national or local guidelines and those who must meet at least one of thefollowing conditions at the time of informed consent.

3. Immunodeficiency

4. Chronic Lung Disease

5. Congenital Heart Disease

6. Down syndrome

7. Born pre-term ≤28 wks Gestation age and aged ≤12 months, or born pre-term >28wks and ≤35 wks Gestation age and aged ≤6 months

8. The participant's parent(s)/legally authorized representative(s) can understand andcomply with the requirements of the protocol including follow-up visits as judged bythe investigator.

9. The participant is available to complete the follow-up period for approximately 19months, which will be approximately 1 year after receipt of 2nd dose of nirsevimab

Exclusion Criteria:

1. Requirement for mechanical ventilation, extracorporeal membrane oxygenation,continuous positive airway pressure (CPAP), or other mechanical respiratory orcardiac support at the time of enrollment

2. A current, active RSV infection at the time of screening and investigational productadministration

3. Any fever (≥100.4°F [≥38.0°C], regardless of route) or acute illness at the time ofprior to investigational product administration

4. Any serious concurrent medical condition (except those resulting in an immunedeficiency condition), including:

5. Known renal impairment

6. Known hepatic dysfunction including known or suspected active or chronichepatitis infection

7. Any seizure disorder or evolving or unstable neurological condition

8. Anticipated cardiac surgery within 5-6 months after enrollment

9. Prior history of a suspected or actual acute life-threatening event

10. Receipt or intended use of palivizumab in the current enrollment season

11. Any known allergy or history of allergic reaction to any component of nirsevimab

12. Any known allergy or history of allergic reaction to immunoglobulin products, bloodproducts, or other foreign proteins

13. Concurrent enrollment in another interventional study, or prior receipt of anyinvestigational agent

14. Anticipated survival of less than 1 year at the time of informed consent

15. Any condition that, in the opinion of the investigator, would interfere with theevaluation of the investigational product or interpretation of study results

16. Children of employees of the Sponsor, clinical study site, or any other individualsinvolved with the conduct of the study, or immediate family members of suchindividuals