Interim 2022/23 influenza vaccine effectiveness: six European studies, October 2022 to January 2023

Background: Between October 2022 and January 2023, there has been diverse circulation of influenza A(H1N1)pdm09, A(H3N2) and B/Victoria viruses in Europe. Aim: To provide interim 2022/23 influenza vaccine effectiveness (VE) estimates from six European studies, covering 16 countries in primary care, emergency care and hospital inpatient settings.Methods: All studies used the test-negative design, although differences in other study characteristics existed, e.g. data sources, patient selection, case definitions and included age groups. Overall and influenza (sub)type-specific VE was estimated for each study using logistic regression adjusted for potential confounders.Results: There were 20,477 influenza cases recruited across the six studies, of which 16,589 (81%) were influenza A. Against A(H1N1)pdm09 (all ages and settings), VE point estimates ranged from 28% to 46%, higher among children <18 years at 49–79%. Against A(H3N2), overall VE ranged from 2% to 44%, also higher among children (62–70%). Against influenza B/Victoria, overall and age-specific VE were ≥50% (84–95% among children).Conclusions: Interim results from six European studies during the 2022/23 influenza season indicate a benefit from influenza vaccination, with higher VE among children. Genetic virus characterisation results and end-of-season VE estimates will contribute to greater understanding of differences in influenza (sub)type-specific results across studies.