A 2008 study from Canada shows that the influenza vaccination has no significant effect on death rates among the elderly. The research, published in the American Journal of Respiratory and Critical Care Medicine, contradicted previous studies showing that getting the flu shot reduces an elderly person's risk of dying from any cause by 50 percent, a claim that other scientists have also challenged as unlikely.

One of the researchers of this new study, Dean T Eurich said,

"Over the last two decades in the United Sates, even while [flu] vaccination rates among the elderly have increased from 15 to 65 percent, there has been no commensurate decrease in hospital admissions or all-cause mortality,

"Further, only about 10 percent of winter-time deaths in the United States are attributable to influenza, thus to suggest that the vaccine can reduce 50 percent of deaths from all causes is implausible in our opinion."

Researchers compared rates of influenza, pneumonia and death among 700 people, 85 percent of them over the age of 64. Half of the participants were given a flu shot, while half were not.

The researchers found that prior to adjusting for any confounding factors, 15 percent of those in the unvaccinated group died, compared with only 8 percent of those in the vaccinated group - appearing to be consistent with the previously reported 50 percent mortality reduction. However, once researchers adjusted for other predictors of mortality such as overall health and socioeconomic status, the difference between the two groups disappeared.

This suggests, the researchers said, that the previously observed decreases in mortality from flu vaccination merely come from the so-called "healthy-user effect" and have nothing to do with the vaccine itself.

The lead researcher Sumit Majumdar explained,

"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,... Such attributes are almost impossible to capture in large scale studies using administrative databases."

It is thus the healthy habits that reduce the risk of death, the researchers suggested, and not the flu vaccine, as previous studies have tried to show.

Details for the study:

Eurich D T et al 2008 Mortality Reduction with influenza vaccine in Patients with pneumonia Outside "flu" Season American Journal of Respiratory and Critical Care medicine Vol 178. pp. 527-533