Many people think of the flu as a seasonal illness that causes fever, cough, and tiredness. However, scientists are learning that influenza can have much more serious effects on the body.
A new study published in Eurosurveillance shows that flu infection can sharply increase the risk of heart attacks and strokes, but vaccination may reduce this danger even if a person still becomes infected.
When the body fights the flu virus, it produces a strong immune response. This response can cause inflammation throughout the body.
While inflammation helps fight infection, it can also make blood vessels less stable and increase the chance of blood clots. These changes can trigger serious events such as heart attacks and strokes, especially in older adults or those with existing health problems.
The research team, led by Croci and colleagues, wanted to understand how big this risk is and whether the flu vaccine can still help after infection. They used detailed health records from Denmark, where each person has a unique identification number that allows researchers to link different types of medical data.
The study included 1,221 adults aged 40 and above who had a first-time hospital admission for a heart attack or stroke after a confirmed flu infection. The researchers examined data over nine flu seasons, from 2014 to 2025. They looked at when infections occurred, whether patients had been vaccinated, and when cardiovascular events happened.
The results showed a clear pattern. The first week after a flu infection was the most dangerous. During this time, the risk of stroke increased three times, and the risk of a heart attack increased five times compared to other periods. This suggests that influenza infection can act as a trigger for these serious conditions.
However, the study also found that vaccination made a significant difference. Among people who had received a flu shot, the increased risk was reduced by about half. This means that even if the vaccine did not stop the infection, it still helped protect the body from severe complications.
The researchers used a special study design that compares each person’s risk at different times. This approach helps reduce the influence of other factors such as lifestyle or long-term health conditions. As a result, the findings are more reliable.
There are some limits to the study. It did not examine how different vaccine types performed or how well the vaccines matched the virus each year.
It also could not determine whether factors like gender or the exact timing of vaccination changed the results. In addition, healthcare systems differ between countries, so the results may not be exactly the same everywhere.
Despite these limitations, the study provides important insights. It shows that the flu vaccine may offer protection in more ways than expected. It not only reduces the chance of infection but also lowers the risk of serious complications when infection occurs.
In reviewing these findings, it becomes clear that influenza vaccination should be seen as an important tool for protecting overall health, not just preventing flu symptoms. The ability to reduce the risk of heart attacks and strokes could have a large impact, especially in older populations.
These results may also support stronger public health policies. Encouraging more people to get vaccinated could help reduce both the spread of flu and the burden of cardiovascular disease. It may also strengthen the economic case for vaccination programs by showing benefits beyond infection prevention.
Overall, this study highlights the hidden dangers of influenza and the broader value of vaccination. While more research is needed, the message is simple and powerful. A flu shot could help save lives not only by preventing illness, but also by protecting the heart and brain during vulnerable periods.
If you care about heart disease, please read studies that herbal supplements could harm your heart rhythm, and how eating eggs can help reduce heart disease risk.
For more health information, please see recent studies that apple juice could benefit your heart health, and results showing yogurt may help lower the death risks in heart disease.
Source: Eurosurveillance (Denmark national registry study).
