Flu vaccines can greatly reduce the risk of life-threatening complications in people with heart failure, an international study led by McMaster researchers shows.

The influenza vaccine reduced the incidence of pneumonia by 42 per cent and hospitalization for any reason by 15 per cent in patients with heart failure, compared to a control group given placebos, first author Mark Loeb says.

The vaccine’s benefits were even more pronounced during flu season, reducing pneumonia cases 50 per cent, and heart attacks, strokes and cardiovascular-related deaths 20 per cent, says Loeb, an infectious disease physician and professor of pathology and molecular medicine.

Researchers tracked more than 5,000 patients with heart failure in 10 countries across Africa, Asia and the Middle East, where few people have a regular influenza vaccination.

Patients received either flu vaccines or a placebo annually between June 2015 and November 2021. While the vaccines reduced the risk of life-threatening flu-related complications, they did not affect the primary outcomes for patients with heart failure.

“These findings highlight the immense importance of vaccinating patients with heart failure against the flu,” Loeb says.

“The vaccine keeps you out of hospital and it really does mean the difference between life and death for patients with heart failure, especially during the peak flu season. These results are yet more proof that vaccines save lives.”

The study is the first clinical trial of the flu vaccine’s effectiveness in patients with heart failure, but previous observational studies found a lower incidence of cardiovascular events and deaths in vaccinated people.

While the flu has long been associated with an increased risk of life-threatening cardiovascular events, Loeb says people with heart failure are already vulnerable to poor health outcomes.

Patients with the condition have a 50 per cent chance of dying within five years, while 20 per cent are hospitalized for heart attacks, strokes and other complications every year.

Eighty per cent of cardiovascular disease occurs in in low and middle-income countries where flu vaccination rates are also low, making them ideal research locations, Loeb says.

Loeb and his colleagues presented their findings to the American College of Cardiology at their annual scientific session in Washington on April 3.

External funding for the study came from the Joint Global Health Trials Scheme (funded by the British government’s Department for International Development, the Medical Research Council, the National Institute for Health Research and the Wellcome Trust), and by the Canadian Institutes for Health Research. Sanofi Pasteur provided the vaccines used in the study.