Influenza and pneumococcal vaccination and risk of stroke or transient ischaemic attack-matched case control study.
BACKGROUND
Evidence that respiratory infections trigger stroke suggests that influenza or pneumococcal vaccination might prevent stroke. We aimed to investigate whether influenza or pneumococcal vaccination or both together were associated with reduced risk of stroke or transient ischaemic attack (TIA).


METHODS
We used a matched 1:1 case-control design with data from the United Kingdom General Practice Research Database. Cases, aged 18 years or above with stroke (fatal or non-fatal) and TIA during September 2001 to August 2009, were compared with controls matched for age, sex, calendar time and practice, adjusting for cardiovascular risk factors, vaccine risk groups, comorbidity and indicators of functional ability.


RESULTS
We included 26,784 cases of stroke and 20,227 cases of TIA with equal numbers of matched controls. Influenza vaccination within-season was associated with 24% reduction in stroke risk (adjusted OR 0.76, 95% CI 0.72 to 0.80) but no reduction in TIA (1.03, 0.98 to 1.09). Stroke risk was significantly lower with early (September to mid-November: 0.74, 0.70 to 0.78) but not later influenza vaccination (mid-November onwards: 0.92, 0.83 to 1.01). Associations persisted after multiple imputation of missing data and sensitivity analysis for unmeasured confounders. Pneumococcal vaccination was not associated with a reduction in risk of stroke (0.98, 0.94 to 1.00) or TIA (1.15, 1.08 to 1.23).


CONCLUSIONS
Influenza vaccination was associated with a 24% reduction in risk of stroke but not TIA. Pneumococcal vaccination was not associated with reduced risk of stroke or TIA. This has important implications for potential benefits of influenza vaccine.
Community and Health Research Unit, University of Lincoln & Lincolnshire Community Health Services NHS Trust, School of Health and Social Care, College of Social Science, Brayford Campus, Lincoln LN6 7TS, UK. Electronic address: nsiriwardena@lincoln.ac.uk.
A Niroshan
AN
Siriwardena
Community and Health Research Unit, University of Lincoln, School of Health and Social Care, College of Social Science, Brayford Campus, Lincoln LN6 7TS, UK. Electronic address: zasghar@lincoln.ac.uk.
Zahid
Z
Asghar
University of Nottingham, Division of Primary Care, School of Community Health Sciences, Floor 13, Tower Building, Nottingham NG7 2RD, UK. Electronic address: carol.coupland@nottingham.ac.uk.
Carol C A
CC
Coupland
D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007252:Influenza Vaccines / Q000627:therapeutic use*; D002546:Ischemic Attack, Transient / Q000453:epidemiology* / Q000517:prevention & control; D008297:Male; D022242:Pneumococcal Vaccines / Q000627:therapeutic use*; D012307:Risk Factors; D020521:Stroke / Q000453:epidemiology* / Q000517:prevention & control; D006113:United Kingdom / Q000453:epidemiology
D007252:Influenza Vaccines; D022242:Pneumococcal Vaccines
Influenza; Influenza vaccination; Matched case-control study; Pneumococcal vaccination; Stroke; Transient ischemic attack