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Flu shot may cut risk of heart problems, analysis finds

Getting your annual flu shot could mean a 55 percent less chance of another heart problem in the coming year, adding to the list of known yet mysterious benefits of the flu vaccine, according to a new analysis published Tuesday.

Dr. Jacob Udell of the University of Toronto and colleagues looked at all the flu vaccine studies they could find that also kept tabs on heart attacks and other cardiovascular events to see if vaccination helped prevent them.

In four studies examined, patients who had suffered recent heart attacks and who were randomly assigned to get flu shots had a 55 lower risk of having another major heart event, Udell and colleagues reported in the Journal of the American Medical Association. 

“This could be a vaccine against cardiovascular events,” Udell said.

He said it was researchers’ hope that the vaccine could work, too, to prevent heart issues for those who have not experienced recent problems. “Potentially everyone," Udell said. 

"In our primary results/findings, of the 6,700 patients, half got the flu vaccine and half the placebo or standard care, only a third of patients had a history of heart disease. But among those who got the flu shot, we saw a 36 percent lower risk of a major cardiac event! Not too shabby.”

The researchers analyzed six trials of 6,735 patients, half women, with an average age of 67. More than a third had a previous history of heart issues. They were re-evaluated an average of eight months after getting flu shots.

In the five published trials, 95 of 3,238 patients receiving the flu vaccine (2.9 percent) developed a major heart problem compared with 151 of 3,231 patents (4.7 percent) treated with a placebo or control within one year of follow-up, the researchers said. 

So why does the vaccine apparently benefit heart patients? 

People who get the flu are at higher risk for heart problems. And the researchers felt the reason is either something specific to the flu itself causing respiratory infections, the immune response of those who have ensuing heart attacks, stroke or congestive failure, or a combination.

“We know that inflammation can trigger plaques to rupture and cause blockage of vessels, which causes heart attacks,” Udell said.

“There is a lot of data that this inflammation does play a role,” Udell added. If true, the findings could provide “one of those missing links” to understanding and combating heart disease. 

“This could be another great tool to help lower that risk even further than what we currently are doing," Udall said.

“We would like to take that second bite of the apple,” he added. 

Dr. William Shaffner, an infectious disease expert at Vanderbilt University Medical Center, said the study clearly shows influenza is a body-wide infection that affects more than just the lungs. It reaches the heart and can worsen underlying conditions. Getting a flu shot for anyone middle-aged or older, or at risk for a heart attack, is an easy step with much clear benefit.

"I wouldn't expect it to have a notable affect on a 22-year-old basketball player," Shaffner added.

Flu activity is still low in the U.S. this year, the Centers for Disease Control and Prevention said. 

The CDC recommends everyone older than age six months get vaccinated annually as the best way to protect against the illness and prevent its spread.