In general, both vaccines are very effective. Prevnar is the more recent introduction into the vaccine schedule (starting in 2000), and research is ongoing. However, it appears that invasive illness from the seven serotypes included in the vaccine has decreased significantly. Pneumovax has been around for decades and is very effective in the elderly. The major drawback with both vaccines is that they only cover some of the more than ninety existing serotypes. While the serotypes included in each vaccine were chosen because they were the most likely to cause infections, there are dozens remaining for which we do not have a vaccine.