Flu shot halves risk of heart attack or stroke in people with history of heart attack, study finds

The flu vaccine may not only ward off serious complications from influenza, it may also reduce the risk of heart attack or stroke by more than 50 per cent among those who have had a heart attack, according to new research led by Dr. Jacob Udell, a cardiologist at Women's College Hospital and clinician-scientist at the University of Toronto. What's more, the vaccine's heart protective effects may be even greater among those who receive a more potent vaccine.

"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," Dr. Udell said. "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."

Published today 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 percent lower risk of a major cardiac event (heart attack, stroke, heart failure, or death from cardiac–related causes) one year later
Had a 55 percent 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, and
Were less likely to have a major cardiac event with a more potent vaccine compared with the standard seasonal vaccine

Dr. Udell carried out this research in collaboration with Dr. Michael Farkouh, senior co-author of the study and Chair of the Peter Munk Centre of Excellence in Multinational Clinical Trials, which is within the Peter Munk Cardiac Centre at the University Health Network.

"If the flu vaccine can reduce the risk of cardiac events, these shots could have considerable impact on cardiac health," said Dr. Udell. However, Drs. Udell and Farkouh 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. Farkouh, who is also director of the Heart and Stroke Richard Lewar Centre at the University of Toronto. "We'll build on this research with a definitive, international trial to conclusively determine whether the flu shot prevents heart attack."

If proven to be a safe and simple prevention method, the impact could be significant for people with or at risk of heart disease and stroke.