Researchers from Switzerland and the UK have found that commonly used pneumococcal polysaccharide vaccines (PPVs) do not seem to be effective for preventing pneumonia.
In many industrialized countries, PPVs are currently recommended to help prevent pneumococcal disease in people aged 65 and over and for younger people with increased risk due to conditions like HIV.
Previous studies have shown conflicting results regarding the efficacy of PPV.
The new findings are based on a study, which 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 researchers examined the reasons why different clinical trials produced different results.
They found that the quality of the studies substantially affected the results.
When only high quality trials were included, there was no evidence that PPVs could prevent pneumonia.
The new study contributes to the ongoing debate around effectiveness of the vaccine.
"Policy makers may therefore wish to reconsider their current recommendations for PPV, especially where routine pneumococcal conjugate immunization has been introduced," said Dr. Matthias Egger from the University of Bern, Switzerland and co-authors.