In view of evidence that influenza can help trigger heart attacks and other cardiovascular events, experts have long wondered if flu vaccination may lower the risk of such events. A meta-analysis released this week, in which researchers sifted through thousands of studies, suggests the answer is yes.
On the basis of five randomized controlled trials (RCTs) that met their selection criteria, an international team of researchers concluded that patients who had a flu shot had a 2.9% risk of a major cardiovascular event in the ensuing year, versus a 4.7% risk for those who were not vaccinated. That suggested that one cardiovascular event would be prevented for every 58 people vaccinated.
Also, when the researchers separately analyzed three trials that involved only volunteers who already had coronary artery disease, they found that the risk reduction was especially pronounced in those who had had a cardiovascular event in the previous year. In that group, vaccinees had about a 10% risk of another event in the ensuing year, versus a 23% risk for those who skipped vaccination.
"Our meta-analysis demonstrated a consistent association between influenza vaccination and a lower risk of cardiovascular events," says the report in the Journal of the American Medical Association (JAMA). "Our findings provide some support for guideline recommendation for influenza vaccination of patients with ACS [acute coronary syndrome]."
Other experts who commented on the study said it was well done and supports an association between flu vaccination and lower cardiovascular risk. But they raised questions about the finding of a much greater risk reduction in those with a history of very recent cardiovascular episodes and called for more rigorous trials.