A meta-analysis of 16 international studies has demonstrated that having recently been infected with influenza virus doubles an individual’s risk of a heart attack. (1)
If you are vaccinated against the influenza virus you have a 29% lower risk of a heart attack. This is greater protection than quitting smoking, lowering your cholesterol with statins and lowering your blood pressure with medication.
A flu vaccine DOES NOT negate the need for quitting smoking and lowering your cholesterol and blood pressure with medications, it simply adds an EXTRA level of protection for you.
The studies in the meta-analysis are all case-controlled studies; not randomised controlled trials. They cannot control for confounding variables and probably shouldn’t be used to draw conclusions about cause and effect but they can show a strong association. The proposed mechanism is that a virus causes a physiological response that increases inflammation of muscle (both skeletal and cardiac) and this might reduce the coronary blood supply, particularly in people who already have compromised coronary blood supply and were already at risk of a heart attack.
Essentially getting sick with a virus puts extra strain on your heart and lungs and that extra strain might be enough to cause a heart attack in many cases.
This supports the observation that that higher mortality rates coincide with peak periods of influenza and pneumonia, even when you discount the deaths directly caused by influenza and pneumonia (2). Madjid and others (2007) confirmed that the risk of dying from acute myocardial infarction and chronic ischaemic heart disease is 1.3 times greater during influenza epidemic weeks (3).
So when you are deciding if you are going to get flu vaccine next year, it is worth considering not only your risk of acquiring a respiratory infection but also your risk of having a cardiovascular event.
Isn’t science grand?
- Barnes, M., Heywood, A. E., Mahimbo, A., Rahman, B., Newall, A. T., & Macintyre, C. R. (2015). Acute myocardial infarction and influenza: a meta-analysis of case–control studies. Heart, 101(21), 1738-1747.
- Reichert, T.A., Simonsen, L., Sharma, A., Pardo, S.A., Fedson, D.S. and Miller, M.A. (2004) Influenza and the Winter Increase in Mortality in the United States, 1959-1999. American Journal of Epidemiology, 160, 492-502. http://dx.doi.org/10.1093/aje/kwh227
- Madjid, M., Miller, C.C., Zarubaev, V.V., Marinich, I.G., Kiselev, O.I., Lobzin, Y.V., Filippov, A.E. and Casscells, S.W. (2007) Influenza Epidemics and Acute Respiratory Disease Activity Are Associated with a Surge in Autopsy-Confirmed Coronary Heart Disease Death: Results from 8 Years of Autopsies in 34,892 Subjects. European Heart Journal, 28, 1205-1210. http://dx.doi.org/10.1093/eurheartj/ehm035