How the flu, COVID-19, and common viruses could raise your risk of heart attack and stroke

Getting sick with the flu or COVID-19 raises the risk of heart attack or stroke in the following weeks, according to a new analysis that maps how viruses can affect heart health.

Researchers have long known that viruses such as human papillomavirus (HPV) and hepatitis B can cause cancer, but links to other health problems, such as heart disease, are more of a mystery.

The latest analysis drew data from 155 studies. It indicates there are heart health risks tied to infections as wide-ranging as influenza, coronavirus, HIV, hepatitis C, and varicella zoster virus, which causes shingles and chickenpox.

“Our study found acute and chronic viral infections are linked to both short- and long-term risks of cardiovascular disease, including strokes and heart attacks,” Kosuke Kawai, the study’s lead author and an epidemiologist at the University of California, Los Angeles, said in a statement.

In the month after a flu diagnosis, people are four times as likely to have a heart attack and five times as likely to have a stroke, according to the study, which was published in the Journal of the American Heart Association.

They are three times as likely to have a heart attack or stroke in the 3.5 months after getting COVID-19, with risks remaining higher for a year after infection, the study found.

Meanwhile, the elevated risks were lower but persistent for people with chronic infections.

Heart attack risks were 60 per cent higher for people with HIV, 27 per cent higher for those with hepatitis C, and 12 per cent higher for those with shingles at least five years later.

Kawai said the findings are “clinically relevant” given the number of people affected by these chronic viral infections.

Globally, there were about 1.3 million new HIV infections in 2024 and about one million new hepatitis C infections are reported annually.

Meanwhile, estimates published in 2021 found that across Europe, there are approximately six to 10 new shingles cases per year for every 1,000 people.

That means “the elevated risk associated with that virus translates into a large number of excess cases of cardiovascular disease at the population level,” Kawai said.

Viral infections trigger the immune system, prompting it to release molecules that increase blood flow to fight off the virus. That causes inflammation – visible as redness, swelling, and warmth – and blood clotting.

However, inflammation and blood clotting can also hinder the heart’s functioning, which could help explain why heart attack and stroke risks remain higher after infections, the researchers said.

They noted that the evidence is still unclear on whether other viruses, including dengue, HPV, cytomegalovirus, which can cause birth defects, and herpes simplex 1, which causes cold sores, raise heart health risks.

There are ways to lower these risks, with vaccination against the flu, COVID-19, and shingles offering promise, the study found. Managing inflammation overall could also be key.

In a 2022 review, for example, people who got a flu shot had a 34 per cent lower risk of dying or being hospitalised for a cardiovascular problem compared with people who got a placebo, or dummy shot.

In general, vaccinations could be especially beneficial for people who already have heart disease or other risk factors, Kawai said.

“Preventive measures against viral infections, including vaccination, may play an important role in decreasing the risk of cardiovascular disease,” Kawai said.