An infection with the influenza virus ("flu") temporarily increases the risk of a heart attack, especially in individuals without a history of hospitalization for heart problems. This is according to a Dutch study led by University Medical Center (UMC) Utrecht among more than 23,000 adults who had a severe influenza infection between 2008 and 2019. To better protect adults without known cardiovascular disease from a heart attack after severe influenza, it should be investigated whether this group would benefit from temporary anticoagulation therapy.

It is well-known that the risk of a heart attack is temporarily increased in the initial period after a severe acute respiratory tract infection. This is probably because such an infection disrupts blood clotting and causes the release of pro-inflammatory molecules. As a result, atherosclerotic plaques become unstable, pieces become detached and these subsequently cause a blockage of a coronary artery. Therefore, in the Netherlands patients with cardiovascular disease (CVD) or people at increased risk of a heart attack (such as those with thrombosis, diabetes or hypertension) receive an annual invitation for an influenza vaccination. Most of them also take anticoagulants and blood pressure medication to lower their heart attack risk. However, it is not clear what effect a severe influenza infection has on the risk of a heart attack in adults without known CVD.

Heart attack risk strongly increased in adults without known CVD

Researchers at UMC Utrecht therefore analyzed the risk of heart attack in a national database among 23,405 adults aged 35 and older who had contracted a severe influenza infection (confirmed by a laboratory test) between 2008 and 2019. The study showed in the first week after a severe influenza infection there was a six-fold increased risk of a heart attack (relative risk 6.16, 95% confidence interval 4.11-9.24). However, in adults without previous hospitalization for heart problems, the risk of a heart attack was as much as 16 times higher, while the risk was only slightly increased in patients with CVD. The researchers explain the observed lower risk of a heart attack in patients with CVD because they already take medications that lower the risk of a heart attack such as anticoagulants and blood pressure-lowering drugs.

In addition to an increased risk for heart attack after a severe influenza infection, the study found that the risk of a heart attack was also increased after a severe infection with the RS virus or other respiratory viruses.

Temporary anticoagulation treatment

Principal investigator Patricia Bruijning-Verhagen, MD PhD, professor of vaccination and infection control epidemiology (Julius Center for Health Sciences and Primary Care, UMC Utrecht) says: "Our study is the first to convincingly demonstrate that adults without known CVD are temporarily at increased risk of a heart attack after a severe influenza infection. To better protect this group, we should investigate in a study if temporary anticoagulation therapy can prevent heart attacks. Patients with a history of CVD already receive such medication as standard, and our study shows that they are better protected. Therefore, adults without known CVD experiencing a severe influenza infection might benefit from temporary anticoagulation treatment to reduce their heart attack risk. In addition, this study also highlights the importance of the flu vaccination to prevent severe disease. The average age in our study was 74 years, whereas in the Netherlands we invite everyone over 60 to annual flu vaccination."

Publication

Boer AR de, Riezebos-Brilman A, Hout D van, Mourik MSM van, Rümke LW, Hoog MLA de, Vaartjes I, Bruijning-Verhagen PCJL, on behalf of the Influenza-MI Study Group. Influenza infection and acute myocardial infarction. NEJM Evidence 2024;3(7)

Editorials

MacIntyre CR, Akhtar Z, Moa A. Influenza vaccine – Low-hanging fruit for prevention of myocardial infarction. NEJM Evidence 2024;3(7)

Dodd LE. Influenza and Acute Myocardial Infarction — Causal Link or Spurious Association? NEJM Evidence 2024;3(7)