Influenza vaccine effectiveness in European primary care pediatric practices: 2022–2024.

Objectives To estimate influenza vaccine effectiveness (VE) in the pediatric population (<18 years) attending primary care in the European Union and European Economic Area in 2022/2023 and 2023/2024. Methods General practitioners swabbed and interviewed patients with acute respiratory tract infection. We conducted a test-negative case-control study and used logistic regression to estimate VE against any influenza and specific (sub)types, overall and by age group, and within the vaccine recommendation target group. Results Among 10 368 children in 2022/23, 3286 (32%) tested polymerase chain reaction-positive for influenza virus; among 9270 children in 2023/24, 1567 (17%) tested positive. Influenza A(H3N2) and B predominated in 2022/23, and influenza A(H1N1)pdm09 in 2023/24. Among the test-negative controls, 17% were part of the vaccine recommendation target group in 2022/23 and 38% in 2023/24. In 2022/23, overall VE against any influenza was 68% (95% CI: 59–76); 57% (95% CI: 26–76) against influenza A(H1N1)pdm09; 54% (95% CI: 33–69) against influenza A(H3N2); 83% (95% CI: 74–90) against influenza B. In 2023/24, overall VE against any influenza was 71% (95% CI: 62–78); 75% (95% CI: 64–83) against influenza A(H1N1)pdm09; 40% (95% CI: 4–64) against influenza A(H3N2); and 92% (95% CI: 63–100) against influenza B. All VE estimates varied by age and vaccine recommendation target group. Conclusions In 2022/23 and 2023/24, more than two-thirds of vaccinated children were protected against primary care-attended influenza infection in Europe. Monitoring VE in children can help inform influenza immunization programs.