If you need extra motivation to get your flu shot this fall, here it is: A new study finds that people battling the flu may also face a temporary spike in their risk of having an acute myocardial infarction (heart attack)—especially if they have no known underlying heart disease.
The study, conducted in the Netherlands and published in NEJM Evidence in June, looked back at the medical records of 401 people, mostly older than 65. All had tested positive for the flu sometime between 2008 and 2019, and had suffered a heart attack during the year before or after that test result. Researchers found that the week following a positive flu test was an especially risky time for the heart: People were six times more likely to suffer a heart attack during that week, versus the year before or after. Of note, the majority of influenza patients must have been quite ill because they were admitted to the hospital at the time of testing.
The findings add to a growing body of evidence connecting flu infection with a short-term rise in heart attack risk. Researchers suspect it may be due to the effects of the influenza virus on blood clotting and inflammation in the arteries—both of which can contribute to heart attacks in some people.
The new study did, however, uncover a surprise: The heightened heart attack risk was primarily seen among people who had never previously been hospitalized for coronary artery disease—a buildup of “plaque” in the heart arteries that can cause severe chest pain, breathing problems, or, if an artery becomes completely blocked, a heart attack.
Among those people, the risk of suffering a heart attack was nearly 17 times greater in the week following a positive flu test, versus the other time periods analyzed. This suggests that a bout with the flu might be particularly dangerous for people with “silent” coronary artery disease (that is, disease that has never been diagnosed). In contrast, the researchers speculate, people with known heart disease are likely to be on medications, including clot-preventing drugs, that might help shield them from the consequences of getting the flu.
Now for the good news: Research also shows that getting vaccinated against the flu may help ward off a heart attack—whether you have a history of heart trouble or not. An analysis in Scientific Reports in November 2023 pooled the results of five clinical trials involving over 9,000 people who were randomly assigned to receive a flu shot or a placebo (a jab with an inactive substance). Over an average of nine months, those who were vaccinated were about one-quarter less likely to suffer a heart attack, and one-third less likely to die of cardiovascular causes, compared with placebo recipients.
Those trials involved people who had already suffered past cardiovascular events, including heart attacks and strokes. But another study in 2023, published in the European Heart Journal, found that flu shots may offer similar protection against first-time cardiovascular trouble, too: Among nearly 194,000 middle-aged and older adults, the risk of having a first heart attack was 33 to 40 percent lower in the four months following a flu shot, versus the rest of the year. The odds of suffering other cardiovascular diseases, including stroke, were also lowered.
The takeaway here is pretty straightforward. Between 100,000 and 710,000 people in the U.S. are hospitalized—and 4,900 to 51,000 die—every year from influenza, the CDC estimates. An annual flu shot is already recommended for nearly everyone to reduce the risk of getting the flu—and especially to reduce the risk of a severe infection that might land you in the hospital. Now we have more evidence than ever that vaccination might also protect your heart. If you’ve been skipping your flu shot, let this be the year you get back on track.
