Study of a Single Intramuscular Dose of Nirsevimab in the Prevention of Hospitalizations Due to Respiratory Syncytial Virus (RSV) Infection in Healthy Term and Preterm Infants During the First Year of Life

The purpose of this study was to determine the efficacy and safety of a single intramuscular (IM) dose of nirsevimab, compared to no intervention, for the prevention of hospitalizations due to lower respiratory tract infection (LRTI) caused by confirmed RSV infection (henceforth referred to as RSV LRTI hospitalizations) in all infants under 12 months of age who were not eligible to receive palivizumab.

The visit frequency was 1 in-person dosing/randomization visit, with monthly safety follow-up electronic contacts through the first 6 months post dosing/randomization for all participants. The study also included a 12-month (Day 366) follow-up telephone call. The D366 follow-up telephone call was the final follow-up telephone call for France, Germany and UK non-reconsented participants. The study included an 18-month (D546) and a 24-month (D731, final telephone call) follow-up telephone call for UK reconsented participants.

12 months post-dosing/randomization for France, Germany and UK non-reconsented participants, 24 months post-dosing/randomization for UK reconsented participants. D01 was the day of randomization (both study groups) and immunization (nirsevimab group).

Eligibility Criteria:
Inclusion Criteria:

* Born at ≥ 29 weeks gestational age and aged 0 to 12 months (calendar age), who entered their first RSV season on the day of inclusion in the study (D01)
* Informed consent form was signed and dated by the parent(s) or other LAR(s) (and by an independent witness if required by local regulations)
* Participant and parent/LAR were able to attend the scheduled visit and to comply with all study procedures

Exclusion Criteria:

* Participants were not eligible for the study if any of the following criteria are met:
* Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive therapy, such as anti-cancer chemotherapy or radiation therapy, within the preceding 6 months; or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3 months)
* Active confirmed RSV infection at the time of dosing/randomization
* Active LRTI at the time of dosing/randomization
* 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
* Laboratory confirmed thrombocytopenia, or known thrombocytopenia, as reported by the parent/LAR, contraindicating intramuscular injection
* Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating intramuscular injection
* Any condition that, in the opinion of the investigator, is at a stage where it might interfere with study conduct or completion
* 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 was not included in the study until the condition has resolved or the febrile event has subsided
* Mother of the infant participant was administered an RSV vaccine during her pregnancy with the infant participant
* Receipt of any monoclonal antibody by the infant participant
* Receipt of immune globulins, blood or blood-derived products in the past 3 months by the infant participant
* Participation at the time of study enrollment or planned participation during the present study period in another clinical study investigating a vaccine, drug, medical device, or medical procedure
* Eligible to receive palivizumab at time of inclusion (as per local guidelines)
* In an emergency setting or hospitalized involuntarily
* Identified as a natural or adopted child of the Investigator or employee with direct involvement in the proposed study

The above information were not intended to contain all considerations relevant to a participant's potential participation in a clinical trial.