The flu vaccine may reduce the risk of heart attack or stroke among those who have had a heart attack by more than 50%, according to new research from Women’s College Hospital and the University of Toronto.

“Our study provides solid evidence that the flu shot helps prevent heart disease in vulnerable patients —with the best protection in the highest risk patients," said Jacob Udell, a cardiologist from Women’s College Hospital and lead author of the study. “These findings are extraordinary given the potential for this vaccine to serve as yearly preventative therapy for patients with heart disease, the leading cause of death among men and women in North America.”

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Published in the Journal of the American Medical Association, the study reviewed six clinical trials on heart health in people who received the flu vaccine. The studies included more than 6,700 patients with a history of heart disease. The researchers found people who received the flu shot:

  • Had a 36% lower risk of a major cardiac event (heart attack, stroke, heart failure, or death from cardiac–related causes) one year later
  • Had a 55% lower risk of a major cardiac event if they had a recent heart attack
  • Were less likely to die from cardiac-related and other causes
  • Were less likely to have a major cardiac event with a more potent vaccine compared with the standard seasonal vaccine.

The researchers caution that a large prospective clinical trial is necessary to confirm the effectiveness and safety of the influenza vaccine as a therapy that will reduce the risk of heart attack or stroke in people with heart disease. The researchers are now organizing this type of clinical trial to follow heart disease patients for up to 12 months after receiving the flu shot.

“These findings are all the ammunition we need to move forward,” said Dr. Michael Farkouh, senior co-author of the study and chair of the Peter Munk Centre of Excellence in Multinational Clinical Trials. “We’ll build on this research with a definitive, international trial to conclusively determine whether the flu shot prevents heart attacks.”