Flu vaccine may lower heart attack and stroke risk after infection

A Danish registry study found vaccinated adults had about half the risk of hospitalization for heart attack or stroke after laboratory-confirmed flu compared with unvaccinated adults. A separate meta-analysis reported fewer heart attacks and heart-related deaths and a 28% lower risk of death overall among people with heart disease or heart failure who were vaccinated.

Researchers analyzed Danish health registry data from the 2015–16 to 2023–24 influenza seasons to examine adults aged 40 and older who had a first-time hospitalization for acute myocardial infarction (AMI) or stroke within a year of laboratory-confirmed flu infection. Of 1,221 such adults identified, 610 had received a flu vaccine and 621 had not. The study reported higher risks of AMI and stroke in the first week after flu infection, and it found that vaccinated participants had about half the risk of heart attack or stroke compared with unvaccinated participants. An accompanying editorial noted that differences between vaccinated and unvaccinated groups could influence the results, and a separate meta-analysis in The American Journal of Cardiology reviewed 23 studies of people with ischemic heart disease or heart failure and reported lower cardiovascular deaths and a 28% lower risk of death overall among vaccinated individuals. Key findings: - In the Danish study, acute myocardial infarction risk rose roughly fivefold and stroke risk rose about threefold in the first week after laboratory-confirmed flu infection, compared with other time periods. - Among the 1,221 adults studied, 610 were vaccinated and 621 were unvaccinated, and vaccinated participants showed about a 50% lower risk of heart attack or stroke in the observation window used. - The meta-analysis of 23 studies including more than 1.1 million people with heart disease or heart failure found fewer heart attacks and heart-related deaths among vaccinated people and a 28% lower overall risk of death. - That same meta-analysis reported no reduced risk for stroke or for overall major adverse cardiovascular events in its pooled results. - An editorial accompanying the Eurosurveillance study raised the possibility of confounding bias from differences between vaccinated and unvaccinated populations. Summary: The studies together point to an association between influenza vaccination and lower rates of certain cardiovascular events and deaths in the populations analyzed. Further research and analysis were noted by authors and editorialists as needed to clarify potential confounding and underlying mechanisms.