Post-licensure safety of nirsevimab from the Canadian National Vaccine Safety (CANVAS) network.

Although clinical trials have shown that nirsevimab is safe, post-licensure safety data from routine clinical settings are lacking. This study describes parent-reported health events occurring within seven days of nirsevimab administration. Post-licensure, active, safety surveillance was conducted during the 2024-25 viral season in Canada, using parent-completed questionnaires distributed 8 days after immunization. Parents or caregivers of 1,559 children completed the survey. A third (454/1,559) of children had received nirsevimab co-administered with routine vaccines. Local injection-site reactions were reported in 140 children (9.0%), 79/454 (17.4%, [95%CI: 14.2-21.3]) when nirsevimab was co-administered and 61/1,105 (5.5% [95%CI: 4.3-7.1]) when nirsevimab was given alone. Injection-site reactions extending beyond the closest joint were uncommon (6/1,559, 0.4%). Health events that prevented daily activities or required healthcare consultation were reported in 38/1,105 (3.4%) cases with nirsevimab administered alone and 19/454 (4.2%) with nirsevimab co-administered. The most reported symptoms were rhinorrhea: 1.8%, cough: 1.7%, feeding/eating changes: 1.6%, fever: 1.6% and diarrhea or change in bowel habits: 1.5%. Rash occurred in 10 children (0.6%). No cases of anaphylaxis were reported. Overall, in this study nirsevimab was well tolerated, with low incidence of health events within seven days of immunization. Results after co-administration support the incorporation of nirsevimab into the routine vaccination schedule. Documenting parent-reported outcomes in post-licensure settings expands the safety data obtained from clinical trials and offers transparent, timely additional reassuring data to enhance parental confidence in RSV antibody interventions.