Dr. Matthias Egger of the University of Bern, Switzerland, and colleagues said that in many industrialized countries, pneumococcal vaccines are currently recommended to help prevent pneumonia in those age 65 and older, and for younger people with increased risk due to conditions like HIV.

The study, a systematic review and meta-analysis, looked at 22 clinical trials, reviews and meta-analyses and more than 100,000 participants from countries in North America, as well as India, Africa, Latin America and the Caribbean.

Unlike other similar studies the authors examined the reasons why different clinical trials produced different results. They found that the quality of the studies substantially affected the results.

The review, published in the Canadian Medical Association Journal, found that when only analyzing high quality trials, there was no evidence that the vaccines could prevent pneumonia.

However, in a related commentary, Dr. Ross Andrews of the Menzies School of Health Research, in Darwin, Australia, said the researchers' conclusions exceed the evidence presented.