Oct. 27 (Bloomberg) -- The present U.S. policy of encouraging people to get seasonal flu shots is supported only by thin medical evidence, a study found.

Research on the efficacy of vaccines on either children or the elderly, two main targets of the policy, are either flawed or don't show a clear benefit, according to the study, published today in the British Medical Journal. The U.S. Centers for Disease Control and Prevention on its Web site says getting a shot is ``the single best way to protect against the flu.''

``The large gap between policy and what the data tell us is surprising,'' the author, Tom Jefferson, coordinator of the Cochrane Vaccines Field, wrote in the paper. The organization, which is part of the U.K.-based Cochrane Collaboration, was founded to facilitate the gathering of evidence on inoculations.

Jefferson examined systematic reviews of known studies of flu vaccines, rather than the results of any single trial, and found the studies had three problems. One was a reliance on trials that were not randomized, giving leeway to systematic errors. The second was an absence of evidence supporting vaccination's efficacy. Lastly, the studies didn't provide a large amount of data on the safety of inactivated vaccines.

This ``policy gap'' is rooted in part in confusion between influenza and influenza-like illnesses, which are often both reported as the same sickness, Jefferson's study found. A lack of surveillance systems to monitor circulating viruses exacerbates this effect. In addition, Jefferson wrote, policy makers tend to intervene with what is available.

This approach leads not only to a waste of resources, but also to a lack of necessary studies on vaccine efficacy, he said.

``It is problematic to raise these concerns at a time when vulnerable people should be getting vaccinated,'' Gordon Lishman, director general of Age Concern, said in a statement. ``We would urge older people to ensure that they receive their vaccination as normal.'' Age Concern is the U.K.'s largest organization working for and with older people.

To contact the reporter on this story: Eva von Schaper in Munich at evonschaper@bloomberg.net.

Last Updated: October 26, 2006 19:01 EDT