When most people think of influenza, they imagine a few days of fever, body aches and bed rest. Flu is often regarded as a threat to the very old, the very young or those with compromised immune systems. The rest of us are reassured we’ll recover quickly. After all, ‘it’s just the flu’.
Seasonal influenza doesn’t appear in the top ten causes of death in the United States. During the 2023–24 flu season, there were an estimated 28,000 flu-related deaths. Why, then, should time and resources be spent combating a seasonal virus when chronic diseases — particularly cardiovascular disease, which claimed more than 919,000 lives in the United States in 2023 — are much more deadly?
Nature Spotlight: Influenza
The reason is that this seemingly vast difference in impact is misleading: infectious and chronic diseases are deeply interconnected. And the collective failure of the health community to understand that relationship has serious implications for patients, their families and the health systems that care for them.
The evidence is compelling. A study in 2018 found that the risk of a heart attack jumps sixfold in the week after a confirmed flu infection1. Another study, involving more than 80,000 adults hospitalized with influenza, found that nearly one in eight experienced an acute cardiovascular event2.
The connection between influenza and a host of cardiovascular conditions is not a surprise. Scientists have long known that the virus affects more than the respiratory tract. It triggers a powerful inflammatory response, sending the immune system into overdrive. This response can activate blood platelets, increasing the risk of blood-clot formation. Fever elevates heart rate and energy demands, and dehydration adds further strain. The result is a physiological storm that can tip vulnerable people — especially those with underlying cardiovascular disease — into crisis.
Cardiac connection
I and many other clinicians care for a lot of people who have had heart attacks during the flu season. But we rarely ask what caused the heart attack during this acute event and, unless people show overt signs of infection, we typically don’t test for influenza. Similarly, when an older adult arrives at hospital with heart failure, or dies suddenly at home, few clinicians pause to consider whether a recent viral illness might have contributed to the event.
When people have thought to look, the findings have been sobering. A 2023 study estimated that, worldwide, nearly 4% of heart-attack deaths among adults aged 50 and over can be attributed to influenza3. This means that strategies to prevent flu infections — including vaccination, hygiene practices and effective communication with the public — could prevent around 300,000 deaths globally.
That realization requires a fundamental shift in how we approach influenza — not as an annual nuisance, but as a real public-health priority.
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