Influenza vaccination status ascertainment and vaccine effectiveness estimation: validity of self-report for current and prior season

Accurate vaccination status ascertainment is fundamental to valid vaccine effectiveness (VE) estimation. We evaluated the accuracy of current and prior seasons self-reported influenza vaccination status among outpatients with acute respiratory illness recruited by the Canadian Sentinel Practitioner Surveillance Network (SPSN) during the 2023-2024 season in Quebec, Canada. Vaccination status was self-reported at specimen collection for influenza virus testing and compared to the provincial vaccination registry. Self-report showed high registry agreement, including sensitivity, specificity, accuracy and kappa statistics for current (91%, 98%, 96%, 0.89) and prior (85%, 95%, 92%, 0.78) seasons vaccination status. Metrics were similar by influenza case status, age, sex and comorbidity with more variation for sensitivity than specificity. Test-negative design estimates of the crude association between influenza case status and current seasons self-reported or registry-based vaccination status did not meaningfully differ, with absolute difference of 2% overall. Findings support self-reported influenza vaccination for timely and valid VE estimation.