Pediatric Influenza Vaccine Effectiveness Against Emergency Visits and Hospitalization in Canada: 2024-2025 and 2025-2026 seasons
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Importance
Influenza causes substantial morbidity in children, yet Canadian data on influenza vaccine effectiveness (VE) in preventing emergency department (ED) visits and hospitalizations are limited.
Objective
To estimate VE against influenza-associated ED visits and hospitalizations among children during the 2024-2025 and 2025-2026 seasons.
Design
Test-negative case-control design.
Setting
Fourteen Canadian pediatric tertiary-care hospitals participating in the Surveillance Program for the Rapid IdeNtification and TracKing of Infectious Diseases in kidS (SPRINT-KIDS) network.
Participants
Symptomatic children aged 6 months to <18 years tested for influenza from October 27, 2024, to June 7, 2025, and from November 2, 2025, to June 13, 2026.
Exposure
At least one dose of current-season influenza vaccine.
Main Outcomes and Measures
VE against laboratory-confirmed influenza A or B associated with an ED visit or hospitalization. VE was estimated using multivariable logistic regression adjusted for age, epidemiologic week, site, and high-risk comorbidity.
Results
The 2024-2025 season included 17,316 encounters (median [IQR] age=41.0 [18.5–82.3] months; 54.0% male), with 4,760 influenza-positive cases (8.9% vaccinated) and 12,556 influenza-negative controls (15.9% vaccinated). The 2025-2026 season included 13,417 encounters (median [IQR] age=33.5 [16.7–74.8] months; 54.1% male), with 4,798 cases (7.6% vaccinated) and 8,619 controls (18.1% vaccinated). VE against any influenza was 47% (95%CI, 40–53%) and 53% (95%CI, 46–59%) in 2024-2025 and 2025-2026, respectively. VE against ED visits was 53% (95%CI, 45–59%) and 57% (95%CI, 49–63%), and VE against hospitalization was 33% (95%CI, 16–47%) and 48% (95%CI, 33–59%) in 2024-2025 and 2025-2026, respectively. VE was lower against influenza A as compared to B in both seasons: 31% (95%CI, 22–39%) vs. 75% (95%CI, 64– 82%) (p<0.001) in 2024-2025; and 42% (95%CI, 32–50%) vs. 64% (95%CI, 55–72%) (p=0.001) in 2025-2026. VE was lower in children aged 10 to <18 years than in those <10 years, particularly among children with comorbidities. Protection against influenza A lasted up to 90 days, whereas it persisted beyond 120 days for influenza B.
Conclusions and Relevance
Influenza vaccines were moderately effective against pediatric ED visits and hospitalizations in both seasons. Routine vaccination should continue to be recommended to prevent hospital-attended influenza.
Key Points
Question
How effective were influenza vaccines against influenza-associated emergency department visits and hospitalizations among Canadian children during the 2024-2025 and 2025-2026 seasons?
Findings
In this test-negative case-control study of 30,733 encounters at 14 pediatric hospitals, vaccine effectiveness against any influenza was 47% in 2024-2025 and 53% in 2025-2026, despite antigenically drifted A(H3N2) subclade K predominance. Effectiveness was lower against influenza A than B and among adolescents.
Meaning
These findings support continued annual influenza vaccination of children, even when substantial antigenic mismatch is anticipated.
