Post-Licensure Safety of Nirsevimab from the Canadian National Vaccine Safety (CANVAS) Network
Bibliographic record
Abstract
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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.003 | 0.005 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".