http://www.theatlantic.com/doc/200911/brownlee-h1n1 But while vaccines for, say, whooping cough and polio clearly and dramatically reduced death rates from those diseases, the impact of flu vaccine has been harder to determine. Flu comes and goes with the seasons, and often it does not kill people directly, but rather contributes to death by making the body more susceptible to secondary infections like pneumonia or bronchitis. For this reason, researchers studying the impact of flu vaccination typically look at deaths from all causes during flu season, and compare the vaccinated and unvaccinated populations.
Such comparisons have shown a dramatic difference in mortality between these two groups: study after study has found that people who get a flu shot in the fall are about half as likely to die that winter—from any cause—as people who do not. Get your flu shot each year, the literature suggests, and you will dramatically reduce your chance of dying during flu season.
Yet in the view of several vaccine skeptics, this claim is suspicious on its face. Influenza causes only a small minority of all deaths in the U.S., even among senior citizens, and even after adding in the deaths to which flu might have contributed indirectly. When researchers from the National Institute of Allergy and Infectious Diseases included all deaths from illnesses that flu aggravates, like lung disease or chronic heart failure, they found that flu accounts for, at most, 10 percent of winter deaths among the elderly. So how could flu vaccine possibly reduce total deaths by half? Tom Jefferson, a physician based in Rome and the head of the Vaccines Field at the Cochrane Collaboration, a highly respected international network of researchers who appraise medical evidence, says: “For a vaccine to reduce mortality by 50 percent and up to 90 percent in some studies means it has to prevent deaths not just from influenza, but also from falls, fires, heart disease, strokes, and car accidents. That’s not a vaccine, that’s a miracle.”
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Jackson’s findings showed that outside of flu season, the baseline risk of death among people who did not get vaccinated was approximately 60 percent higher than among those who did, lending support to the hypothesis that on average, healthy people chose to get the vaccine, while the “frail elderly” didn’t or couldn’t. In fact, the healthy-user effect explained the entire benefit that other researchers were attributing to flu vaccine, suggesting that the vaccine itself might not reduce mortality at all. Jackson’s papers “are beautiful,” says Lone Simonsen, who is a professor of global health at George Washington University, in Washington, D.C., and an internationally recognized expert in influenza and vaccine epidemiology. “They are classic studies in epidemiology, they are so carefully done.”
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