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| |  Flu Shot Does Not Reduce Risk of All-Cause Mortality in Elders NEW YORK -- August 29, 2008 -- The widely-held perception that the influenza vaccination reduces overall mortality risk in the elderly does not withstand careful scrutiny, according to a study in the September issue of the American Journal of Respiratory and Critical Care Medicine. The vaccine does confer protection against specific strains of influenza, but its overall benefit appears to have been exaggerated by a number of observational studies that found a very large reduction in all-cause mortality among elderly patients who had been vaccinated. "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," said Dean T. Eurich, PhD, School of Public Health, University of Alberta, Edmonton, Alberta. "Over the last 2 decades in the United Sates, even while vaccination rates among the elderly have increased from 15% to 65%, there has been no commensurate decrease in hospital admissions or all-cause mortality. Further, only about 10% of winter-time deaths in the US are attributable to influenza, thus to suggest that the vaccine can reduce 50% of deaths from all causes is implausible in our opinion." Dr. Eurich and colleagues hypothesised that if the healthy-user effect was responsible for the mortality benefit associated with influenza vaccination seen in observational studies, there should also be a significant mortality benefit present during the off-season as well. They analysed clinical data of 704 patients aged 65 years and older from 6 hospitals in Alberta. The patients were admitted to the hospital for community-acquired pneumonia during non-flu season; half of the patients had been vaccinated, and half had not. Each vaccinated patient was matched to a non-vaccinated patient with similar demographics, medical conditions, functional status, smoking status, and current prescription medications. In examining in-hospital mortality, they found that 12% of the patients died overall, with a median length of stay of approximately 8 days. While analysis with a model similar to that used in past observational studies indeed showed that patients who were vaccinated were about half as likely to die as unvaccinated patients, a finding consistent with other studies, they found a striking difference after adjusting for detailed clinical information, such as the need for an advanced directive, pneumococcal immunisations, socioeconomic status, as well as sex, smoking, functional status, and severity of disease. Controlling for those variables reduced the relative risk of death to a statistically nonsignificant 19%. Further analyses that included more than 3,400 patients from the same cohort did not significantly alter the relative risk. The researchers concluded that there was a difficult to capture healthy-user effect among vaccinated patients. "The healthy-user effect is seen in … 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," said principal investigator Sumit Majumdar, MD, University of Alberta. "Such attributes are almost impossible to capture in large scale studies using administrative databases." Finally, Dr. Majumder said, the findings are a reminder to researchers that "the healthy-user effect is everywhere you don't want it to be." SOURCE: American Thoracic Society
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