A new study adds to the body of research showing that flu shots do not reduce the risk of death.

While an influenza vaccination will still protect against certain types of the flu, researchers in Alberta, Canada, suggest that the mortality benefit may have been exaggerated. After studying more than 700 elderly patients in Canadian hospitals, researchers say that any reduction to the overall risk of dying conferred by the vaccine is statistically insignificant, if it is even there at all. Half of those patients had received a vaccine andhalf had not.

Researches say that many variables in earlier research onall-cause mortality and influenza vaccines were not considered. They also point out that vaccination rates among American seniors have increased from 15% to 65% over the last 20 years, but there has not been a related drop in overall mortality rates. The results of their research can be found in the first September issue of the American Journal of Respiratory and Critical CareMedicine.