Benefits of flu shots for reducing deaths less than thought: study

The flu shot does help protect against specific strains of influenza but its ability to help prevent deaths among the elderly may have been exaggerated, a new study suggests.

Over the last 20 years in the U.S., vaccination rates among the elderly have increased from 15 to 65 per cent, but hospital admissions and death rates from all causes have not declined proportionately, said Dean Eurich, a clinical epidemiologist and professor at the school of public health at the University of Alberta.

Previous reports of a reduction in mortality rates linked to flu shots were based on observational studies.

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

To investigate, Eurich and his colleagues analyzed data from people 65 or older who were hospitalized for pneumonia during the flu and non-flu season. Each vaccinated person was compared to a non-vaccinated person with similar demographics and medical conditions.

Healthy-user effect

After controlling for factors that were not considered or were not available in previous studies reporting a mortality benefit, Eurich's team concluded the benefit was very small and may be attributed to the healthy-user effect.

The healthy-user effect applies to people who are informed about their health and do everything they can to stay healthy, like watching what they eat, exercising regularly, taking medications as prescribed and getting vaccinated, said Dr. Sumit Majumdar, the study's principal investigator and a medical professor at the university.

The researchers hypothesized that if the healthy-user effect was responsible then there should be a difference in mortality benefit during the off season.

In the first September issue of the American Journal of Respiratory and Critical Care Medicine, the team reported 12 per cent of patients died in hospital.

After controlling for details such as pneumococcal immunizations, socioeconomic status, as well as sex, smoking, and severity of disease, the mortality benefit seen in previous studies was reduced to a statistically non-significant level of 19 per cent, the researchers said.

Vaccinating health-care workers

Despite the findings, Majumdar recommended that people at high risk, such as those with chronic respiratory diseases, health-care workers and family members who care for elderly patients should still be vaccinated.

Health departments could also focus on practices such as hand washing, vaccinating children and vaccinating health-care workers, for which there is more evidence of benefits, the researchers said.

Last year, health officials in eastern Ontario said only 56 per cent of staff at acute-care facilities such as hospitals get the shot, a level they called "worrisome."

In 2007, a group representing infectious diseases specialistsalso called for health-care workers to either get an annual flu shot ornote their refusal in writing.

According to Health Canada, 4,000 to 8,000 Canadians die of flu-related pneumonia each year.