Getting a flu shot could reduce heart attack risk by up to 55 percent, according to a new review of studies published in Journal of the American Medical Association (JAMA).
What’s more, people who were vaccinated against influenza had lower risk for other major cardiovascular events, including stroke, heart failure, and death from cardiac causes, compared to those given a placebo injection, the researchers reported. The analysis pooled data from six randomized clinical trials involving 6,735 patients.
“The biggest benefit of influenza vaccine was seen in those at highest cardiovascular risk, such as people who have had a recent heart attack,” reports lead researcher Jacob Udell, MD, MPH, FRCPC, clinical scientist and cardiologist at Women’s College Hospital and Toronto General Hospital.
“These findings suggest that flu vaccine may also be a vaccine against heart attacks and strokes,” says Dr. Udell. However, the review, which involved combing through thousands of influenza vaccine studies published between 1947 and August 2013, doesn’t prove a cause-and-effect relationship.
A number of studies show a strong link between upper respiratory infections (including flu) and increased risk for cardiovascular events, says Amy Doneen, RN, ARNP, medical director of the Heart Attack & Stroke Prevention Center in Spokane, Washington.
“Up to 91,000 people die annually from heart attacks and strokes triggered by influenza,” says Doneen. “Published data also suggest that if you have plaque in your arteries, coming down with an upper respiratory infection puts you at three to four times higher risk for a heart attack or stroke during the first three days of the infection.”
This may explain why the review found that flu shots are such a powerful weapon against cardiac perils. When the research team analyzed outcomes within one year of being vaccinated (versus getting a placebo), they found that:
The culprit is inflammation, our immune system’s response to flu (or other infections). “Cholesterol plaque inside the arterial wall due to heart disease is like kindling,” explains Doneen. “Inflammation in the arteries lights the match, which can lead to a plaque rupture.”
If that happens, a clot typically forms in an attempt to heal the rupture in the arterial wall. However, if the clot is large enough, it can block a coronary artery—potentially igniting a heart attack—or a blood vessel in the brain, leading to an ischemic stroke.
In addition, inflammation increases the amount of fluid in the blood vessels, adds Dr. Udell. “In people with cardiovascular disease, especially if they’re frail and debilitated, fluid overload can cause heart failure, as well as increased pressure inside the blood vessels that could lead to bleeding in the brain.”
In 2006, the American Heart Association and the American College of Cardiology issued a joint scientific advisory recommending annual flu shots for people with heart or vascular disease, citing “the growing body of evidence that influenza vaccination is protective against cardiovascular events.”
The Centers for Disease Control and Prevention (CDC) advises annual vaccination for everyone age 6 months or older, ideally in October (the start of the flu season). Yet fewer than 50 percent of those most at risk—heart patients—get flu shots, reports Dr. Udell.
One common misconception is that the shot causes the flu. That’s impossible, because vaccines given by needle contain inactivated (non-infectious) virus or no virus at all (as is true of recombinant flu vaccine, according to the CDC).
“You may get some mild, transient achiness, which means your body is mounting an immune response,” says Dr. Udell. “In other words, the vaccine is working.” The shot is about 60 percent effective at preventing seasonal flu, and is extremely safe, with only one in a million people experiencing serious complications, he reports.
“If you have plaque in your arteries, getting vaccinated could save your life,” adds Doneen. And that’s also true for people without heart disease, since flu kills up to 49,000 Americans a year, according to the CDC.
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