Study Questions Flu Shot's Mortality Protection for Elderly

FRIDAY Aug. 29, 2008 -- Canadian researchers are challenging the widely held belief that flu shots help protect older people from potentially deadly diseases such as pneumonia.

While the researchers say the vaccine does protect against certain strains of influenza, its overall benefit seems to have been exaggerated by so-called observational studies that found a big reduction in "all-cause mortality" among older patients who'd gotten a flu shot.

The new research was expected to be published in the first September issue of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.

For the new study, the researchers included more than 700 "matched" people 65 and older, half of whom had received a flu shot and half who had not. After compensating for a variety of factors that the researchers said weren't considered or available in the earlier studies, the study authors concluded that any "all-cause mortality" benefit "if present at all, was very small and statistically non-significant and may simply be a healthy-user artifact that they were unable to identify."

"While such a reduction in all-cause mortality would have been impressive, these mortality benefits are likely implausible. Previous studies were likely measuring a benefit not directly attributable to the vaccine itself, but something specific to the individuals who were vaccinated -- a healthy-user benefit or frailty bias," Dean T. Eurich, a clinical epidemiologist and assistant professor at the University of Alberta School of Public Health, said in a university news release.

Added the study's principal investigator, Dr. Sumit Majumdar, an associate professor in the faculty of medicine and dentistry at the University of Alberta: "The healthy-user effect is seen in what doctors often refer to as their 'good' patients -- patients who are well-informed about their health, who exercise regularly, do not smoke or have quit, drink only in moderation, watch what they eat, come in regularly for health maintenance visits and disease screenings, take their medications exactly as prescribed and quite religiously get vaccinated each year so as to stay healthy. Such attributes are almost impossible to capture in large scale studies using administrative databases."

The Canadian researchers said their study has wide-ranging implications.

For instance, because the earlier studies showing mortality reductions were erroneous, "this may have stifled efforts at developing newer and better vaccines, especially for use in the elderly," the study authors said.

And for policy makers, efforts directed at "improving quality of care are better directed at where the evidence is, such as hand-washing, vaccinating children and vaccinating health-care workers," the authors concluded.

More information

To learn more about flu vaccine, visit the U.S. Centers for Disease Control and Prevention.

Posted: August 2008


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