Seasonal flu vaccination reduces MI risk
MedWire News: Results from a UK study suggest that seasonal influenza vaccination reduces the risk for a first acute myocardial infarction (MI).
Writing in the Canadian Medical Association Journal, A Niroshan Siriwardena (University of Lincoln) and team explain: "Significant increases in acute MI occur during peak winter incidence of pneumonia, influenza, and influenza-like syndrome, particularly during years dominated by epidemic rather than nonepidemic influenza A. This association supports the notion that the increase is caused by influenza rather than cold weather."
They add: "Although several observational studies, as well as two randomized controlled trials, suggest a positive effect of influenza vaccine in preventing acute MI, they provide insufficient and conflicting evidence."
To investigate further, the researchers studied data from the UK General Practice Research Database on 16,012 patients, aged at least 40 years, who suffered a first acute MI between 2001 and 2007.
Influenza vaccination rates among these MI patients were compared with those in a control group of 62,694 patients who did not suffer a heart attack and were matched for age, gender, general practice, and calendar time (month corresponding to index date of acute MI).
In total, 8472 (52.9%) MI patients and 32,081 (51.2%) controls had been vaccinated against influenza during the previous year.
After accounting for variables such as the presence of cardiovascular risk factors, medication use, general practice attendance, and being in an influenza vaccination target group, the researchers found that influenza vaccination during the previous year was associated with a 19% reduced risk for MI, compared with non-vaccination.
Influenza vaccination during the current flu season was also associated with a reduced risk for MI compared with non-vaccination, at an adjusted odds ratio of 0.80.
Further analysis showed that early seasonal influenza vaccination (September to mid-November) was associated with a 21% reduced risk for MI within the same season, while vaccination after mid-November was associated with a 12% reduced risk, compared with non-vaccination.
Pneumococcal vaccination was not associated with a reduced risk for acute MI.
Siriwardena and team conclude: "Influenza vaccination but not pneumococcal vaccination is associated with a reduced rate of first acute MI."
They add: "This association and the potential benefit of early seasonal vaccination need to be considered in future experimental studies."
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By Mark Cowen