The influenza vaccine can significantly reduce the risk of a flu-related heart attack or stroke, even among folks who become infected after vaccination, a new study reports.

The systemic inflammation caused by a flu infection is known to increase short-term risk of heart problems, and the flu vaccine has been shown to reduce this risk by preventing infection in the first place, researchers report in the April issue of the journal Eurosurveillance.

But this new study shows that the vaccine can even help people who wind up with the flu despite getting the jab.

Vaccinated folks have half the heightened risk of heart attack or stroke faced by those who catch the flu without the vaccine’s protection, the study found.

“If confirmed by additional studies in other settings, this would strengthen the case for prioritizing influenza vaccination among people at risk of heart disease or stroke,” concluded the research team led by Roberto Croci, an epidemiologist at the European Center for Disease Prevention and Control in Stockholm.

For the study, researchers tracked more than 1,200 adults 40 or older in Denmark who’d landed in the hospital with a heart attack or stroke within a year of coming down with the flu. These cases occurred between 2014 and 2025.

Two-thirds (65%) of the patients had suffered a stroke, and the rest (35%), a heart attack. About half of the cases occurred after the patient had been vaccinated against the flu.

Results showed that within the first week of catching the flu, people’s risk was three times higher for suffering a stroke and five times higher for a heart attack.

But this risk was cut by half for people who caught the flu but had been vaccinated against it for that season, researchers found.

“Our findings add to the evidence that influenza vaccination confers cardiovascular protection,” researchers wrote. “In this study, prior vaccination halved the excess risk of acute myocardial infarction or stroke following breakthrough influenza infection.”

Researchers noted that the study didn’t account for differences in effectiveness between flu vaccines, which change year-by-year depending on which strains are projected to be the most dangerous during any given season.

The study also couldn’t assess whether vaccination timing or gender affected patients’ outcomes.