DEAR DOCTORS: I can't stop thinking about what my doctor said when I got my flu shot last fall. I'm a 55-year-old man, and I have a history of high blood pressure. He said the flu shot will give me extra protection against having a heart attack. What is the connection?
DEAR READER: When we think about the possible complications of the flu, they typically include a sinus infection, ear infection or an escalation to bronchitis or pneumonia. But an emerging body of research now points to a link between infection with the influenza virus and an increased risk of having a heart attack or stroke. This connection has proven to be particularly strong in people living with hypertension and heart disease, and in those who have previously had a heart attack. In 2018, a Canadian study published in the New England Journal Of Medicine found that the inflammation that occurs during a case of the flu can trigger a heart attack. In that study, the researchers analysed seven years of medical data collected from adults of all ages with confirmed cases of influenza who had been hospitalised. They found that in the week following their diagnosis, patients were six times more likely to have a heart attack than in the year before their hospitalisation or the year after.
A separate study, conducted two years later by the US Centers for Disease Control and Prevention, looked at health data from 80,000 adults over the course of eight flu seasons. Each of them had confirmed flu cases that were severe enough to require hospitalisation. The data showed that 12% of the adults in the study had a heart attack or died of heart failure in the week after their flu diagnosis.
This year, researchers in Spain looked at the same question in adults 50 and older. In that population, even mild flu translated to a doubled risk of heart attack, and also stroke, in the two weeks following diagnosis. In patients with heart disease, the risk of heart attack, stroke or heart failure quadrupled.
As anyone who has experienced the prolonged misery of the flu knows, it's a serious infection. Inflammation causes a wide range of symptoms, including fever, cough, headache, sore throat, congestion, muscle aches and pains, and fatigue and exhaustion. Now researchers suspect that influenza infection may also have an adverse effect on arterial plaque. That's the build-up of cholesterol within the walls of the vessels that return blood back to the heart. It is thought that the widespread inflammation in an influenza infection can cause ruptures in existing plaques. This causes the formation of a blood clot, which then impedes or completely blocks blood flow and leads to a heart attack.
These studies bolster the existing guidance regarding the benefits of getting an annual flu shot. And while it's already spring and time to think about sunblock, in many parts of the country, significant flu activity continues as late as May. Particularly for those at higher risk, it's still not too late to get a flu shot. Universal Features Syndicate
Dr Eve Glazier is an internist and associate professor of medicine at UCLA Health. Dr Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health.
