Flu Shot May Reduce Stroke Risk

Aimee Simone, Assistant Editor
Published Online: Wednesday, March 19, 2014
Research from the United Kingdom suggests that getting the influenza vaccine, especially early in the flu season, significantly reduces one’s risk of stroke.

In addition to the known benefits of receiving the flu shot, the results of a study conducted in the United Kingdom suggests the vaccine may also protect against stroke.
 
Previous research has investigated the relationship between influenza vaccine and stroke risk, but results have been inconsistent. Aiming to improve the evidence, the current study, published in the March 10, 2014, issue of Vaccine, set out to determine whether influenza vaccination, pneumococcal vaccination, or a combination of the two are associated with a reduced risk of stroke or transient ischemic attack (TIA).
 
The researchers compared the vaccination status of patients aged 18 years and older from the United Kingdom General Practice Research Database who had experienced a stroke or TIA from September 2001 through August 2009 with matched controls who had not experienced either cardiovascular event. The analysis adjusted for cardiovascular risk factors, vaccine risk groups, comorbidity, and indicators of functional ability.
 
The study included 26,784 cases of stroke and 20,227 cases of TIA. The results indicated that influenza vaccination was associated with a 24% reduced risk of stroke during that season. The reduction in stroke risk was observed 6 months after vaccination and for strokes that occurred between September and March. This association remained significant even after multiple analyses accounting for unmeasured cofounders and missing data.
 
The association was strongest for patients who were vaccinated early in the season, from September to mid-November. In addition, the reduction in stroke risk was slightly greater among patients aged 65 and older than it was in younger patients, although this difference was not statistically significant. There was no association between influenza vaccination and reduced risk for TIA, and pneumococcal vaccination was not associated with a reduction in risk for either stroke or TIA.
 
The study authors suggest that their results support current influenza vaccination recommendations, with stroke prevention as a potential added benefit. They also note that their findings could help improve health outcomes if they lead to greater vaccination coverage. However, they note that their results do not prove a cause-and-effect relationship between influenza vaccination and reduced stroke risk.

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