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Influenza vaccinations reduce the risk of stroke by about a quarter, Vaccine reports.

The analysis included 26,784 strokes, 20,227 transient ischaemic attacks (TIA) and equal numbers of matched controls using a UK general practice database. After adjusting for cardiovascular risk factors, vaccine risk groups, co-morbidity and functional ability, influenza vaccination reduced stroke risk by 24 per cent but did not affect TIA risk. Pneumococcal vaccination did not affect the risk of either stroke or TIA.

The reduction was strongest with immunisation early in the flu season: vaccination between September and mid-November reduced stroke risk by 26 per cent. However the 8 per cent reduction with influenza vaccination from mid-November onwards was not statistically significant.

No significant difference emerged in vaccination’s benefit in people aged at least 65 years (26 per cent reduction) and those aged under 65 years (20 per cent reduction). The reduced stroke risk persisted throughout the same flu season, but did not last beyond a year after vaccination.

“The causes of stroke are not fully understood. Classical risk factors like age, smoking and high blood pressure can account for just over half of all cases,” said lead investigator Niro Siriwardena, professor of primary and pre-hospital healthcare at the University of Lincoln. “Our study showed a highly significant association between flu vaccination and reduced risk of stroke within the same flu season.

“The results were consistent with our previous research into heart attack risk. Further experimental studies would be needed to better understand the relationship between flu vaccination and stroke risk. However these findings reinforce the value of the UK’s national flu vaccination programme with reduced risk of stroke appearing to be an added health benefit.” (Vaccine)