The risk of heart attack or stroke spikes in the weeks following a bout of flu or COVID-19, according to new research. 

People are four times more likely to have a heart attack in the month after having the flu, and five times more likely to have a stroke. With COVID, the likelihood of a heart attack or stroke triples in the 14 weeks after illness, and remains at a higher level for a year.

Certain chronic viral infections — shingles (herpes zoster), HIV, and hepatitis C — can raise cardiovascular risks for years.

“Previous research has shown that viruses may elevate heart risks, but we took a comprehensive look at many studies to compare how much different viruses affect the chances of having a cardiac event,” says the lead study author, Kosuke Kawai, ScD, an adjunct associate professor in the division of general internal medicine and health services research at the David Geffen School of Medicine at the University of California in Los Angeles.

Viruses Threaten the Heart as Well as the Lungs

While scientists have been studying the effects of viral illness on heart health, the general public may not be aware of the connection, says Robert H. Hopkins, MD, the medical director of the National Foundation for Infectious Diseases, who was not involved in the research.

Many people think of influenza, for instance, as mainly a respiratory disease. “But influenza also infects tissues in systems beyond the lungs, including the heart,” Dr. Hopkins says. “Influenza also reduces resistance to and can predispose people to bacterial infections, which can cause pneumonia and sepsis. All of these mechanisms can have profound cardiovascular impacts.”

Viruses Can Have Long-Term Impacts

For Orly Vardeny, PharmD, a professor of medicine at the University of Minnesota in Minneapolis, the findings regarding chronic viral infections and cardiovascular risk were especially notable.

“I was surprised by the amount of research available for viruses that aren’t as well recognized for their associations with heart disease, such as hepatitis C virus and herpes zoster,” says Dr. Vardeny, who was not involved with the study.

In studies comparing long-term risk (average of more than five years) of cardiovascular emergencies in people with certain chronic viral infections, versus similar people without the infection, the researchers found:

• HIV increased the risk of heart attack by 60 percent and the risk of stroke by 45 percent.
• Hepatitis C increased the risk of heart attack by 27 percent and the risk of stroke by 23 percent.
• Shingles increased the risk of heart attack by 12 percent and the risk of stroke by 18 percent.

Kawai notes that this higher risk among people who’ve had shingles can persist for 10 years after infection.

Some viruses were not spotlighted in the study; the authors say more research is needed on heart disease risk and RSV, HPV (human papillomavirus), hepatitis A, and others.

Why Do Viral Infections Affect the Heart?

The immune system’s natural response to viral infections includes the release of molecules that trigger and sustain inflammation and promote the tendency of blood to clot, both of which may last long after the initial infection has resolved.

The study authors note that both inflammation and blood clotting can reduce the ability of the heart to function properly, and this may help explain the increased heart attack and stroke risk.

Inflammation also contributes to the formation and rupture of plaques (hardened deposits of cholesterol, fat, and other substances) in arteries, which can lead to heart attacks and strokes.

Protect Yourself From Viruses This Holiday Season

The study suggests that preventive measures against viral infections may reduce the likelihood of cardiovascular crises.

“People should recognize that vaccines are the best means of protection from an overwhelming systemic response that may lead to multiple organ dysfunction,” says Amit Mahajan, MD, a national medical spokesperson for the American Lung Association, and the medical director of interventional pulmonology and the complex airways disease program for the Inova Health System.

“The holidays can be stressful, and viral infection may further increase stress hormone levels in the body, which can increase the workload on the heart, especially in vulnerable groups such as older adults and those with chronic health conditions,” says Vardeny.

Big meals and increased alcohol use during the holidays further strain the heart, according to the American Heart Association, and colder temperatures can restrict blood flow.

Proper hygiene, such as proper handwashing, may also keep viruses from spreading. Vulnerable groups such as people with heart disease may consider wearing a mask when traveling, especially when taking public transportation.

“This study demonstrates that there are many viruses that can cause cardiovascular injury — and other viruses need more study to determine if they have similar impact,” says Hopkins. “Protecting yourself by vaccination or other good health habits could result in lower risk for cardiovascular disease. This is just one more reason to get vaccinated for your own better health.”