But Garratt said that statement was incorrect.
"This study did not measure risk of heart attack in vaccinated and non-vaccinated people. It measured rates of vaccination among heart attack patients and those without heart attack," said Garratt, noting it was a useful way to look for a connection between heart attacks and flu shots, but not to draw the conclusion drawn by the author.
Siriwardena stressed, however, that, "I think it is important again to say again that we found an association rather than proving cause-and-effect. We also found a greater association between reduction of heart attack and early vaccination."
Krumholz, who is also a cardiology professor at Yale, said that the U.S. Centers for Disease Control and Prevention is recommending everyone be vaccinated in any event.
"The study is timely because we're trying to encourage people to get vaccinated," said Krumholz. "The findings reinforce the recent clear evidence that vaccinations are beneficial."
The American Heart Association and the Association of American Cardiologists both recommend flu shots for people who have heart disease or have a high risk of developing cardiovascular problems, Krumholz added.
The main theory about the benefits of flu shots, Garratt said, is that an infection can trigger a rupture of plaque inside arteries, causing a heart attack. Plaques are hardened fats and other substances that can build up on artery walls and cause blockages.
Flu also raises inflammation levels in the body, possibly setting the stage for a heart attack, Krumholz noted.
For the study, published in the September issue of the Canadian Medical Association Journal, information was taken from a medical record database covering about 5 percent of the population in England and Wales. Both study cases (heart patients) and controls were at least 40 and had at least five-and-half years of medical records befo
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