The flu has been associated with a significantly increased risk of a cardiac event like heart attack or stroke. But the flu vaccine can reduce that risk, even if a vaccinated person still contracts the flu. Unfortunately, Americans with heart disease, who already have a significantly elevated risk of heart attack and stroke, do not have high rates of flu vaccination. Under 50 percent of Americans with heart disease who are under 65 years of age get the flu vaccine, according to new research in the Journal of the American Heart Association.
The flu is a respiratory illness, and can cause other respiratory complications like bronchitis, pneumonia, and bacterial infections. Research has now shown that deaths from cardiovascular events spike at the same time that flu epidemics do, and that in the week following a flu infection, people are six times more likely to have a heart attack compared to any other time of the year.
Various studies have connected flu and heart attacks; one study including over 300,000 people showed that 11.5 percent of people hospitalized with the flu also had a cardiac event; another study including about 90,000 people found basically the same rate: 11.7 percent.
Cardiac events seem to be linked to the flu because of inflammation. The immune response to infection can be massive, and has to be carefully controlled. When immune activity is ramped up because of something like the flu, blood clots can occur because the vasculature is flooded with immune cells and molecules. Blood pressure may increase, the heart can swell, the arteries are under stress and they become vulnerable to breakage. Ruptures in the arteries may cut off oxygen, causing a heart attack, or stroke. The flu can also worsen symptoms of heart disease.
Even when the seasonal flu vaccine is not great at stopping flu infection, it still reduces the likelihood that people will be hospitalized for the flu. Vaccinated people are 37 percent less like to be hospitalized and 82 percent less likely to go to the ICU.
When people with acute coronary syndrome were vaccinated, their rate of cardiovascular events was about 9.5 percent, but the rate was 19 percent in those who were unvaccinated. If people got the flu, their risk of a cardiovascular event was 4.7 percent if unvaccinated, which dropped to 2.9 percent in vaccinated people.
The researchers stressed the importance of getting a flu vaccine, especially in anyone with a chronic health condition. Seasonal flu vaccines for this year are now available.