Evaluate the Safety and Efficacy of Nirsevimab in Healthy Preterm and Term Infants in China

Inclusion Criteria:

1. Healthy Chinese preterm and term infants in their first year of life and born ≥ 29 weeks 0 days GA (infants who have an underlying illness such as cystic fibrosis or Down syndrome with no other risk factors are eligible)
2. Infants who are entering their first RSV season at the time of screening
3. Written informed consent and any locally required authorization obtained from the subject's parent(s)/legal representative(s) prior to performing any protocol-related procedures, including screening evaluations
4. Subject's parent(s)/legal representative(s) able to understand and comply with the requirements of the protocol including follow-up visits as judged by the Investigator
5. Subject is available to complete the follow up period, which will be approximately 1 year after receipt of investigational product

Exclusion Criteria:

1. Any fever (≥ 100.4°F [≥ 38.0°C], regardless of route) or acute illness within 7 days prior to investigational product administration
2. Any history of LRTI or active LRTI prior to, or at the time of, randomization
3. Known history of RSV infection or active RSV infection prior to, or at the time of, randomization
4. Any drug therapy (chronic or other) within 7 days prior to randomization or expected receipt during the study with the exception of: a) multivitamins and iron; b) infrequent use of over-the-counter (OTC) medications for the systemic treatment of common childhood symptoms (eg, pain relievers) that may be permitted according to the judgment of the Investigator
5. Any current or expected receipt of immunosuppressive agents including steroids (except for the use of topical steroids according to the judgment of the Investigator)
6. History of receipt of blood products, or immunoglobulin products, or expected receipt through the duration of the study
7. Hospitalization at the time of randomization, unless discharge is expected within the 7 days after randomization
8. Known renal impairment
9. Known hepatic dysfunction including known or suspected active or chronic hepatitis infection
10. History of CLD/bronchopulmonary dysplasia
11. Clinically significant congenital anomaly of the respiratory tract
12. CHD, except for children with uncomplicated CHD (eg, patent ductus arteriosus, small septal defect)
13. Chronic seizure, or evolving or unstable neurologic disorder
14. Prior history of a suspected or actual acute life-threatening event
15. Known immunodeficiency, including human immunodeficiency virus (HIV)
16. Mother with HIV infection (unless the child has been proven to be not infected)
17. Any known allergy or history of allergic reaction to immunoglobulin products, blood products, or other foreign proteins, or history of allergic reaction
18. Receipt of palivizumab or other RSV mAb or any RSV vaccine, including maternal RSV vaccination
19. Receipt of any monoclonal or polyclonal antibody (for example, hepatitis B immune globulin, IV immunoglobulin) or anticipated use during the study
20. Receipt of any investigational product
21. Concurrent enrollment in another interventional study
22. Any condition that, in the opinion of the Investigator, would interfere with evaluation of the investigational product or interpretation of study results
23. Children of employees of the Sponsor, clinical study site, or any other individuals involved with the conduct of the study, or immediate family members of such individuals