London ? A new analysis of 40 years of research provides more evidence that flu shots are not as effective in the elderly as commonly believed. But health officials said older people should still be vaccinated.

The research, done by an international collaboration of scientists known as the Cochrane Review Group, found the vaccine is only about 28 percent effective when given to people over 65. Older people are particularly vulnerable to influenza.

The findings are similar to those of a study done by U.S. National Institutes of Health that found flu shots for the elderly in the United States had not saved lives.

However, the World Health Organization and the U.S. Centers for Disease Control and Prevention said the findings, published Thursday on the Web site of the Lancet medical journal, do not change their recommendation that elderly people get the shots.