Outpatients’ interim estimates of 2025–2026 seasonal influenza vaccine effectiveness in the Community of Madrid (SiVIRA-MAD Group Data)

In June and July 2025, a rapid increase in the incidence of influenza A(H3N2) subclade K raised awareness about a possible vaccine mismatch. We estimated the mid-season influenza vaccine effectiveness (IVE) against laboratory-confirmed influenza in outpatient settings in the Community of Madrid for the 2025/26 season. Individuals attending to primary care with acute respiratory infection (ARI) and tested for influenza were enrolled in the study. A test-negative design was used to calculate IVE. From week 40 of 2025 to week 2 of 2026, data from 763 ARI cases were included in the study. The adjusted IVE for gender, age, chronic diseases, month of onset, and RSV/COVID-19 coinfection was 52.74% (95% CI: 13.67% to 74.13%) overall, 46.46% (95% CI: −34.34% to 78.67%) for A(H1N1)pdm09 and 65.20% (95% CI: 18.92% to 85.06%) for A(H3N2). Despite the suspected influenza vaccine mismatch, IVE for A(H3N2) type was high.