Influenza vaccination is associated with a reduced risk of stroke

Vascular death rates and hospitalizations for stroke are increased during influenza epidemics. Influenza vaccination may prevent stroke. We investigated whether influenza vaccination is associated independently with reduced odds of stroke and whether effects are confined to stroke subgroups and winter seasons and shared by other vaccinations.

During 18 months, we performed standardized interviews assessing vaccination status, risk factors, health-related behavior, and socioeconomic factors in 370 consecutive patients with ischemic or hemorrhagic stroke or transient ischemic attack (TIA) and 370 age- and sex-matched control subjects selected randomly from the population.

Influenza vaccination during the last vaccination campaign was less common in patients (19.2%) than control subjects (31.4%; P<0.0001). After adjustment for vascular risk factors, education, health-related behavior and other factors, influenza vaccination (odds ratio [OR], 0.46; 95% CI, 0.28 to 0.77) but not other combined recent vaccinations (OR, 0.80; 95% CI, 0.42 to 1.43) were associated with reduced odds of stroke/TIA. Significant effects were found in men, older subjects (>65 years), subjects with previous vascular diseases, and regarding ischemic stroke; nonsignificant trends existed in women, younger subjects, and regarding hemorrhagic stroke. In etiologic subgroups of cerebral ischemia, similar effects were found. No protective effects were found during summer months; however, results also varied considerably between both winter seasons examined.

These results support the hypothesis that influenza vaccination may be associated with reduced stroke risk. However, residual confounding cannot be excluded, and interventional studies are required to evaluate the role of influenza vaccination in stroke prevention.