Stroke victims get fewer flu shots

PARIS, Jan. 31 (UPI) -- Researchers in Paris say there may be a connection between getting flu shots and reducing your chances of getting a stroke.

The physicians say while other factors may affect their study results, people who appeared less likely to get strokes not only got flu shots but also paid more attention to health care in general and had a higher socioeconomic status.

A stroke or brain infarction -- now also called a "brain attack" by some medical centers -- happens when blood is prevented from reaching brain tissue and some tissue dies as a result. Fatty deposits that break loose from blood vessel walls are most commonly the cause of the blockage.

Researchers studied 90 patients admitted for stroke Bichat Hospital in Paris during the flu season. The researchers then created a control group by randomly selecting people from voting lists in Paris and matching them to stroke victims by age, gender and where they lived.

Many other possible influences on stroke were considered, including patient histories of hypertension, diabetes, smoking, pathologic cholesterol levels, antibiotic use, heart conditions and types of employment.

The results showed people who had a stroke were less likely to have gotten a flu shot. The study said 46 percent of stroke cases had received a flu shot in the vaccination season before their strokes, whereas 59 percent of the control group had been vaccinated against influenza. When the scientists looked at the pattern of flu shots over the past five years, they found 41 percent of people who had strokes had been vaccinated every year for the past five years while 56 percent of the control had received all five annual shots.

Researcher Pierre Amarenco, chair of Bichat Hospital's Department of Neurology and the stroke center at Denis Diderot University, expressed concerns about the study to other experts who reviewed the work. Amarenco pointed to lifestyle and socioeconomic status as possible contributors to the results, which appear in the February issue of the journal Stroke, published by the American Heart Association.

An AHA press release quoted Amarenco as saying: "We found the reduction in stroke risk to be around 40 percent for those who were vaccinated, which would be a major advance in stroke prevention if further studies confirm these results."

In an interview with United Press International, Amarenco said: "We did not calculate a reduction of incidence of stroke, but a reduction of the occurrence of vaccination in our stroke population."

The results were received with the same caution the authors expressed. Thomas Carmichael, an attending physician at the University of California at Los Angeles Stroke Center, told UPI, "The patient number is small and the effect is small. It's interesting but it really is very far from conclusive."

Carmichael emphasized the better health care the control group had received.

"It suggests that is a really significant confounder, and that may be the entire explanation of the study," he said.

During infections, some blood serum proteins called acute phase reactants increase. A correlation has been noted between this rise and heart attacks. It is thought the same may be true for strokes, although the mechanism is not known, Carmichael said. The effect of infections on strokes and heart attacks has been more closely studied in Europe than in the United States, he added.

Robert Wityk, director of the clinical stroke service at Johns Hopkins Hospital in Baltimore, Md., and an assistant professor of neurology and medicine at Johns Hopkins Medical School, said: "I don't think anyone is going to accept it right off the bat and make any changes in practice based on this," Wityk said.

Unknown factors could be causing the results, given the way the study was designed and research has shown people who get strokes are more likely to have had a cold or a viral infection in the preceding week or two, Wityk said.

"So there's probably something about infection that might trigger a stroke in somebody who's going to have a stroke anyhow. ... If there's an infection that increases the blood clotting during a particular week that might make it more likely to happen then, than during the following week."

(Reported by Joe Grossman in Santa Cruz, Calif.)