Assessing vaccine coverage and delivery strategies for influenza and COVID-19 among Italian healthcare workers: A 2015-2023 case study.

Healthcare workers (HCWs) are essential in preventing and managing infectious diseases. Despite their critical role, vaccination coverage among HCWs remains suboptimal, endangering not only patient safety and healthcare system efficiency, but also HCWs' own health due to their frequent exposure to infectious agents. This study examines a decade of influenza vaccination trends and recent COVID-19 vaccine co-administration patterns at a major Italian hospital, aiming to identify factors affecting vaccine acceptance and evaluate organizational strategies to enhance vaccination uptake. A retrospective cohort study analyzed vaccination data from 6,341 hCWs between 2015 and 2023, examining acceptance rates across different vaccination delivery models. Mixed effects logistic regression models evaluated the impact of sociodemographic and professional factors and organizational approaches on vaccine acceptance. Results showed influenza vaccination peaked at 46% during the first COVID-19 year, before declining to pre-pandemic levels. Co-administration rates increased significantly, with a 118.94% rise between 2021 and 2022. Different delivery models significantly influenced vaccine acceptance: "open-day" events significantly boosted influenza vaccine acceptance (OR 22.29, 95% CI [18.22; 27.27]), while the hospital outpatient service proved optimal for co-administration (OR 61.03, 95% CI [30.97; 120.25]). This study reveals important patterns in vaccination behavior and organizational effectiveness. The observed decline in influenza vaccination after the COVID-19 peak suggests vaccine fatigue and reduced risk perception due to widespread preventive measures. The success of different delivery models indicates that healthcare institutions should implement multiple, complementary vaccination strategies tailored to specific contexts and workforce preferences, while maintaining continuous educational support to ensure sustained vaccine coverage.