Association Between Influenza Vaccination and Reduced Risk of Brain Infarction

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Abstract
Because infections subsequent to influenza may play a role in promoting the complications of atherosclerotic disease and may also induce hypercoagulation, we hypothesized that influenza vaccination may protect against brain infarction. During the influenza epidemic period we studied 270 subjects, including 90 consecutive patients older than 60 years admitted to the hospital for brain infarction and 180 population-based controls, matched for age, sex, and district of residency in Paris. We conducted a structured interview on whether they had been vaccinated during the last influenza vaccination campaign or every year during the 5 last years. We found significantly fewer vaccinated subjects during the last vaccination campaign among patients with brain infarction than among controls (46.7% versus 59.4%; P=0.036) and fewer patients vaccinated every year during the last 5 years (41.1% versus 56.1%; P=0.017). After adjustment for age, traditional risk factors, and recent use of antibiotics, the risk of stroke was reduced in the subjects vaccinated during the year of the study and in those vaccinated during the last 5 years, with an odds ratio of 0.50 (95% CI, 0.26 to 0.94; P=0.033) and 0.42 (95% CI, 0.21 to 0.81; P=0.009), respectively. Similar associations were observed in cases and controls free of previous cardiovascular history. Subjects younger than 75 years and subjects free of risk factors or in high social class were significantly less often vaccinated than controls. Influenza vaccination may protect against brain infarction by reducing infections or may identify a subgroup of patients at low risk for stroke because of a better lifestyle. These results give rise to a new hypothesis for research into stroke prevention.