Influenza vaccination and risk of dementia: a systematic review and meta-analysis.

BACKGROUND The association between influenza vaccination and a reduction in dementia was unclear with inconsistent evidence. We aimed to evaluate the association between influenza vaccination and dementia risk in the overall population and the high-risk populations for dementia, such as patients with chronic kidney syndrome (CKD), chronic obstruction pulmonary disease (COPD) and vascular disease. METHODS We performed a systematic review and searched PubMed, Embase and CENTRAL from inception to 6 April 2025. The risk of bias was assessed using the Newcastle-Ottawa Scale. A random-effects model meta-analysis was executed. RESULTS We included eight cohort studies with 9,938,696 subjects. Except for one study, the risk of bias of all other included studies was low. Influenza vaccination was associated with a reduced risk of incident dementia in high-risk populations for dementia, but not in the overall population (HR 0.93; 95% CI: 0.86-1.01). For high-risk populations, more than one dose of influenza vaccination showed an association with a lower risk of incident dementia (2-3 doses: HR 0.84; 95% CI: 0.76-0.92; ≥ 4 doses: HR 0.43; 95% CI: 0.38-0.48). CONCLUSION Influenza vaccination was associated with a decreasing risk of incident dementia in a dose-response manner.