Getting a yearly flu vaccine may do more than protect against influenza. A new large analysis suggests it could also reduce the risk of heart attacks.
The study, published in the journal BMC Public Health, combined data from 15 previous studies involving a total of 23.5 million people.
The research team, led by scientists from Zhejiang Chinese Medical University in China, looked at several types of observational studies, including cohort studies, case-control studies, and one self-controlled case series.
Most of the participants were older adults, generally between 57 and 77 years of age.
After pooling the data, the researchers found that people who received a flu vaccine had an 18% lower chance of experiencing a myocardial infarction, also known as a heart attack, compared to those who were not vaccinated.
The results were statistically significant, meaning the finding is unlikely to be due to chance. The estimated reduction ranged from 14% to 22%.
The protective link appeared consistent across different types of studies and groups of patients. When researchers looked at people aged 70 and older and those younger than 70, both age groups showed a similar reduction in heart attack risk after vaccination.
The same pattern was seen in people who had previously suffered a heart attack and those who had not. In both cases, flu vaccination was associated with lower odds of another or first heart attack.
The authors note that heart attacks tend to occur more often during flu season. Viral infections like influenza can trigger widespread inflammation in the body and may affect the lining of blood vessels.
This inflammation and stress on the cardiovascular system could increase the likelihood of a heart attack, especially in people who already have underlying heart disease. By preventing influenza infection, vaccination may reduce this inflammatory response and lower cardiovascular strain.
However, the researchers caution that the findings do not prove that the flu shot directly prevents heart attacks. All of the included studies were observational, which means they can show associations but cannot confirm cause and effect.
There was also limited information about how often participants were vaccinated or exactly when they received the vaccine.
Despite these limitations, the large size of the study and the consistency of the results across different populations strengthen the evidence that flu vaccination may have heart-protective benefits. The authors call for further research to better understand how influenza vaccination might reduce heart attack risk and to explore the biological mechanisms involved.
For now, the findings provide another possible reason for older adults and people at risk of heart disease to consider getting their annual flu shot.
