Study Finds Nirsevimab Safe for RSV Prevention in Infants
Written By : Medha Baranwal
Medically Reviewed By : Dr. Kamal Kant Kohli
Published On 2026-05-26 15:30 GMT | Update On 2026-05-26 15:30 GMT
Canada: A large Canadian study indicates that nirsevimab, a long-acting monoclonal antibody used to prevent respiratory syncytial virus (RSV), is generally safe and well-tolerated in infants.
The research, conducted by the University of British Columbia and published in Human Vaccines & Immunotherapeutics, analyzed safety data from 1,559 infants during the 2024–25 RSV season. Findings were based on parent-completed questionnaires collected within one week after immunization, which showed that most post-immunization effects were mild and temporary, and serious adverse events were rare.
The study was led by Marina Viñeta Paramoa and colleagues, who aimed to generate real-world safety data following the rollout of nirsevimab outside controlled clinical trials. Using the Canadian National Vaccine Safety (CANVAS) network, researchers conducted active surveillance by distributing questionnaires to parents or caregivers eight days after immunization to capture early health events.
Key Findings:
- The analysis included 1,559 infants, with about one-third receiving nirsevimab along with routine childhood vaccines.
- This allowed comparison between infants receiving nirsevimab alone and those receiving it in combination with other vaccines.
- Local injection-site reactions were reported in 9% of infants overall.
- Such reactions were more common with co-administration (17.4%) compared to nirsevimab alone (5.5%).
- More severe injection-site reactions extending beyond the nearest joint were rare.
- A small proportion of infants experienced health events that interfered with daily activities or required medical attention.
- These events occurred in 3.4% of infants receiving nirsevimab alone and 4.2% of those receiving it with other vaccines.
- The most frequently reported symptoms were mild and included runny nose, cough, feeding changes, fever, and diarrhea, each affecting fewer than 2% of infants.
- Skin rash was reported in less than 1% of cases.
- No cases of anaphylaxis were reported.
The findings indicate that nirsevimab’s real-world safety profile is consistent with clinical trial data. Injection-site reactions were lower when given alone compared to routine vaccines and similar when co-administered, supporting its use alongside standard immunizations.
The study has limitations, including participant concentration in one province and reliance on parent-reported data, which may introduce bias. It also assessed only short-term outcomes within one week, limiting the detection of rare or delayed effects.
Despite this, the study offers important real-world evidence supporting nirsevimab’s safety in infants, helping fill data gaps and strengthening confidence among caregivers and clinicians, while supporting its inclusion in RSV prevention strategies.
Reference:
Viñeta Paramo M, Kiely M, Valiquette L, Muller MP, McGeer A, Isenor JE, Sadarangani M, Kellner JD, Vanderkooi OG, Marty K, Lavoie PM, Bettinger JA. Post-licensure safety of nirsevimab from the Canadian National Vaccine Safety (CANVAS) network. Hum Vaccin Immunother. 2026 Dec;22(1):2658377. doi: 10.1080/21645515.2026.2658377. Epub 2026 Apr 28. PMID: 42048598; PMCID: PMC13128022.
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