A study published in the Canadian Medical Association Journal has found an association between getting seasonal flu shots, and a reduced risk of heart attacks.
We included 78 706 patients, of whom 16 012 were cases and 62 694 were matched controls. Influenza vaccination had been received in the previous year by 8472 cases (52.9%) and 32 081 controls (51.2%) and was associated with a 19% reduction in the rate of acute myocardial infarction...
The authors also found that earlier vaccination, between September and mid-November, was more beneficial than receiving vaccinations later in the season, finding a reduction in risk of heart attacks of 21% in people getting their shots earlier, versus 12% in people who vaccinated late. The advantage held up even when the authors performed an analysis that corrected for pre-existing illnesses, since people with health problems are more likely to get seasonal flu shots.
It has long been known that heart attacks are more common in winter than summer. But this study suggests that maybe influenza can be a trigger for heart attacks, rather than just the cold weather.