The Impact of the COVID-19 Pandemic on Influenza Vaccination: A Multi-Year Interrupted Time Series Analysis

To assess temporal changes in influenza vaccination coverage and evaluate differences by age and gender in the context of the COVID-19 pandemic. We conducted a population-based interrupted time series analysis using data from Clalit Health Services in Israel. Adults aged ≥21 years were followed over 11 influenza seasons (2014-2015 to 2024-2025). Annual vaccination rates were stratified by age group (21-40, 41-64, ≥65) and gender. Segmented linear regression assessed changes before and after the pandemic onset. Counterfactual modeling estimated expected vaccination rates in the absence of the pandemic. Vaccination coverage declined from 26.2% (2014-2015) to 17.7% (2024-2025), despite a temporary rise to 28.7% in 2020-2021. Post-pandemic, rates decreased by 2.3 percentage points annually (p = 0.0013). The most pronounced drop was among adults aged ≥65, from 64.8% to 49.2%. Declines were observed across all age and gender groups. Interaction models showed no significant gender differences, but greater declines with increasing age. Counterfactual analysis estimated that 2024-2025 coverage was 5.7 percentage points lower than expected. The COVID-19 pandemic was associated with a sustained decline in influenza vaccination uptake. Targeted strategies are needed to rebuild trust and restore routine immunization, especially among older adults.