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Study Finds Flu Shots Prevent Strokes

Risk is 40% lower among people who were vaccinated

THURSDAY, Jan. 31, 2002 (HealthDayNews) -- A flu shot can protect you against a stroke, a French study finds.

The risk was 40 percent lower for people who had the influenza vaccine compared to a carefully matched group of people who didn't, researchers at the Denis Diderot University in Paris report in the February issue of Stroke, a journal of the American Heart Association.

"There is a theory linking infectious disease with atherosclerosis [hardening of the arteries]," explains Dr. Pierre Amarenco, professor of neurology at the university and a member of the study group. "Especially, it says that infections can promote or trigger occlusions of blood vessels, either coronary arteries or brain arteries."

"We hypothesized that patients vaccinated against influenza may be at less risk of brain infarction [stroke] because they are at less risk of infection. So, we asked patients admitted for brain infarction whether they had been vaccinated against influenza and compared them with control persons who were matched for age, sex and place of residence. We found that the stroke patients were much less likely to be vaccinated than the controls."

That result verifies what was once regarded as a heretical link between the flu vaccine and protection against both stroke and heart attack after it was first reported in 2000 by Dr. S. Ward Casscells, a professor of medicine and leader of a research group at the University of Texas at Houston Medical School.

"They thought we were nuts," Casscells says of the reaction to a study showing that flu vaccination reduced the risk of second heart attacks by 67 percent in patients 65 and older. "This is now a real field."

The French study is the latest of at least four finding a relationship between the flu vaccine and lower risk of cardiovascular disease, Casscells says. Other studies have found a reduction in the incidence of sudden death and of first heart attacks, he says.

Amarenco cautions that his study of 270 people does not establish the cause of the reduction.

"The interpretation of the results could be that influenza vaccination prevents stroke," he says. "But another explanation may be that vaccinated patients may well be those subjects who are much more concerned about health care, good exercise, a low-fat diet and so on. Vaccinated patients may in fact define a group of patients who are at less risk for stroke."

However, Casscells says work by his group points to a protective effect of the vaccine. In the first study, he says, patients were asked if they had flu shots every year, an indication of good health practices.

"The ones who got the flu vaccine the year of the study were protected whether or not they were in the habit of getting the vaccine every year," he says.

And laboratory work with mice, described in a paper that will soon be published, supports that view, Casscells says.

"We studied atherosclerotic mice," he says. "An infection caused a big exacerbation of the atherosclerosis. Pneumonia stirs up the immune system in a bad way. Either it causes thickening of the blood or it makes the immune system mistake the artery for a virus, or both."

The new research is a revival of an idea that was once widely held, but later abandoned.

"Fifty years ago, physicians linked influenza with a risk of heart attack," he says. "We have just raised that issue again."

What To Do

"The central message for readers should be to get the vaccine, because the vaccine not only prevents influenza but also consequences that could include brain infarction," Amarenco says.

For information about influenza and the flu vaccine, consult the Centers for Disease Control and Prevention. Meanwhile, the National Stroke Association has information on risk factors for a brain attack.

SOURCES: Interviews with Pierre Amarenco, M.D., professor, neurology, Denis Diderot University, Paris; S. Ward Casscells, M.D., professor, medicine, University of Texas at Houston Medical Center, Houston; February 2002 Stroke
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