Influenza vaccination may help protect against heart attack and stroke even when it does not prevent people from getting the flu, according to a new study published in Eurosurveillance.
For the study, researchers led by a team from the Statens Serum Institut in Copenhagen looked at data from a Danish health registry from the 2015–16 to 2023–24 flu seasons to identify adults aged 40 years and older who experienced a first-time hospitalization for acute myocardial infarction (AMI) or stroke within a year of laboratory-confirmed flu infection. Of the 1,221 identified adults, 610 were vaccinated, and 621 were not.
Heart attack risk increases 5-fold after infection
In analyzing the data, the researchers found that AMI risk increased roughly fivefold, and stroke risk rose about threefold in the first week after flu infection compared with other time periods. But flu vaccination appeared to significantly reduce that risk. The findings showed that the risk of heart attack or stroke was reduced by half in participants who had received a flu vaccine compared with unvaccinated participants.
Previous research has shown a link between cardiovascular events and flu infection, which triggers short-term inflammation throughout the body and can make blood more likely to clot. For example, one Canadian study found that the risk of a heart attack was about six times higher in the first week after testing positive for the flu. Similar findings have been reported in Spain and the Netherlands.
Vaccine lowers overall mortality risk by 28%
A separate meta-analysis published this week in The American Journal of Cardiology looked at 23 studies that included more than 1.1 million people with heart disease or heart failure to see whether getting a flu shot helped protect against adverse cardiovascular events. The findings suggest that people who were vaccinated had fewer heart attacks and heart-related deaths than those who weren’t vaccinated, and they had a 28% lower risk of death overall.
While the data showed no reduced risk for stroke or overall major adverse cardiovascular events, the benefits of flu vaccination were consistent across age, disease type, study design, and duration of follow-up.
“Influenza vaccination markedly lowers mortality and provides cardiovascular protection in patients with IHD [ischemic heart disease] or HF [heart failure], supporting annual vaccination as an effective secondary prevention strategy,” write the researchers.
Prioritizing vaccine high-risk groups
In an editorial accompanying the Eurosurveillance study, Jeffrey C. Kwong, MD, writes that while the findings show promise, more research is needed. “Could [the protective effect] be simply due to differences between the vaccinated and unvaccinated populations i.e. confounding bias?” he writes.
“Vaccinated and unvaccinated individuals may differ in important ways, such as the presence of cardiovascular disease risk factors and engagement in health-promoting behaviours.”
