October 21, 2015
Stroke Reduction: Bonus from Influenza Vaccination

Lincoln, United Kingdom—Getting vaccinated against influenza does more than just reduce the risk of the debilitating infection or even hospitalization for some of the common side effects, such as pneumonia.

It also can reduce the chances of suffering a stroke, according to a new British study finding that the likelihood of a cerebrovascular event is significantly reduced for the 2 months after receiving a flu vaccine. The research, published recently in the journal Vaccine, indicates that the chance of having a first stroke fell by around a fifth in the first 59 days after being immunized.

Greater protection was provided by vaccines administered earlier in the flu season, according to the University of Lincoln researchers. Background information in the study notes that stroke can be triggered by respiratory infections, including influenza, leading the researchers to question whether influenza vaccination would reduce that risk.

To find an answer, the study team used a self-controlled case series design, extracting records from the General Practice Research Database (GPRD) of adults who had a stroke—fatal or nonfatal—from September 2001 to May 2009.

With 17,853 eligible individuals who received one or more influenza vaccinations and experienced a stroke during the observation period, results found 36% fewer cases of stroke in the first week after flu vaccination compared to a “baseline” population; the drop was 30% in the second week. Stroke cases were 24% lower than baseline in the third and fourth weeks, declining to 17% between 29 days and 59 days after immunization against the flu.

The study also indicates that early vaccination, defined as between September 1 and November 15 in the UK flu season, was more effective in stroke prevention than a vaccination received after mid-November.

“Our findings support current recommendations for the flu vaccination in people at high risk, but with the added effect of stroke prevention,” explained lead author Professor Niro Siriwardena, who also is a general practitioner. “Our study demonstrated that the earlier the vaccination is delivered the greater the linked reduction in stroke risk, so this should also encourage early vaccination.”

The study could have broader implications, according to the researchers. Another recent study agrees with them.

A report published online recently by the journal Neurology notes that influenza, colds, and other minor infections may temporarily increase stroke risk in children, but that the risk can be decreased by routine childhood vaccinations.

The study finds that children who were inadequately vaccinated were at a higher risk of stroke than those who had most or all of their routine vaccinations.

“If our results hold up in further studies, controlling infections like colds and flu through hand-washing and vaccines may be a strategy for preventing stroke in children,” study author Heather J. Fullerton, MD, MAS, said in a University of California San Francisco press release.

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