The purpose of this study is to describe the safety and efficacy outcomes associated with the use of nirsevimab, administered as per routine clinical practice, in neonates and infants aged 0 to 12 months born during or entering their first RSV season and in children up to 24 months of age who remain vulnerable to severe RSV disease through their second RSV season.

Study duration: up to 16 months, including 10 months of enrollment and 6 months of follow-up

• Treatment duration: 1 day; 1 intramuscular (IM) injection

• Visit frequency:

  • 1 in-person visit for immunization (Visit [V] 01) at Day (D) 1.
  • 3 phone call visits (V2, V3 and V4) at D31 (+ 14 days), D91 (+ 14 days) and D181 (+14 days) respectively.

Inclusion Criteria:

Neonates and infants aged 0 to 12 months on the day of inclusion and born during or entering their first RSV season OR children up to 24 months of age on the day of inclusion who remain vulnerable to severe RSV disease through their second RSV season

Exclusion Criteria:

Participants are excluded from the study if any of the following criteria apply:

• Known systemic hypersensitivity to any of the study intervention components, or history of a life-threatening reaction to the study intervention used in the study or to a product containing any of the same substances
• Known thrombocytopenia, as reported by the parent(s)/legally acceptable representative(s), contraindicating intramuscular injection
• Known bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating intramuscular injection
• Chronic illness that, in the opinion of the investigator, is at a stage where it might interfere with study conduct or completion
• Active LRTI on the day of study intervention administration
• Active RSV infection on the day of study intervention administration
• Moderate or severe acute illness/infection (according to investigator judgment) or febrile illness (temperature ≥ 38.0°C [≥ 100.4°F]) on the day of study intervention administration. A prospective participant should not be included in the study until the condition has resolved or the febrile event has subsided
• Receipt of palivizumab or other RSV monoclonal antibody or any RSV vaccine in the same RSV season than inclusion in the study
• Mother of the participant was administered an RSV vaccine during her pregnancy with the participant
• Receipt of immune globulins, blood or blood-derived products in the past 3 months
• Receipt of any investigational drug in the last 30 days prior to the inclusion in the study
• Participation at the time of study enrollment or in the 4 weeks preceding the study intervention administration or planned participation during the present study period, in another clinical study investigating a vaccine, drug, medical device, or medical procedure

Note: The above information is not intended to contain all considerations relevant to a potential participation in a clinical trial.

Qualified researchers may request access to patient level data and related study documents including the clinical study report, study protocol with any amendments, blank case report form, statistical analysis plan, and dataset specifications. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants. Further details on Sanofi's data sharing criteria, eligible studies, and process for requesting access can be found at: https://vivli.org