Influenza Vaccination and Short‐Term Risk of Stroke Among Elderly Patients With Chronic Comorbidities in a Population‐Based Cohort Study

ABSTRACT The protective effect of influenza vaccination on stroke risk has been inconclusive. In this study, we aimed to investigate the impact of influenza vaccination on the 1‐year risk of stroke in individuals aged 60 years and older with COPD and hypertension or diabetes mellitus. We conducted a retrospective cohort study in four districts of Shanghai, China, from August 2017 to July 2019. Data were collected from various information systems related to chronic disease management, cardiovascular reporting, and immunizations. The incidence of stroke within 1 year was compared between vaccinated and unvaccinated chronic disease patients. Cox proportional hazards regression was used to calculate hazard ratios (HRs). Sensitivity analysis was performed using the Poisson regression model to examine the association between influenza vaccination and stroke incidence, and propensity score matching was employed to address confounding. We found that influenza vaccination was associated with a lower risk of stroke during the two influenza seasons, 2017–2018 (adjusted HR, 0.27; 95% CI, 0.10–0.73) and 2018–2019 (adjusted HR, 0.46; 95% CI, 0.21–1.02). The results from the Poisson regression model (RR, 0.26; 95% CI, 0.10–0.70) were consistent with those obtained from the Cox model analysis. The reduction in stroke risk associated with influenza vaccination ranged from 54% to 73%. Our findings suggest that influenza vaccination is associated with a lower 1‐year risk of stroke in individuals with chronic illnesses, compared to those who are not vaccinated.