The initial pre-licensing clinical trials of a pneumococcal capsular polysaccharide involved a comparison study of the effectiveness of a 6-valent polysaccharide vaccine against a 12-valent polysaccharide vaccine. The study involved South African gold miners between the ages of 16 and 58, a population noted to be at a higher risk for pneumococcal pneumonia. The 6-valent vaccine was reported to be 76 percent effective while the 12-valent vaccine was found to be 92 percent effective against the particular pneumococcal strains found in the vaccine.
The long-term effectiveness of the vaccine was not measured as the study was limited to only one year. An additional polysaccharide vaccine effectiveness study involving both a 6-valent and 13-valent polysaccharide vaccine found a 79 percent reduction in pneumococcal pneumonia and an 82 percent reduction in pneumococcal bacteremia caused by the strains found in the vaccine.
In the United States, two post-licensing trials on the effectiveness of the original 14-valent pneumococcal polysaccharide vaccine in the elderly or persons with chronic medical conditions found the vaccine to be ineffective against bronchitis and pneumonia.
Additional research on the effectiveness of the pneumococcal polysaccharide vaccine based on the CDC’s pneumococcal surveillance system found the vaccine to be 57 percent effective against the serotypes found within PNEUMOVAX23 (PPSV23) in persons six years of age and older, between 65 and 84 percent effective in persons with chronic illness (e.g. diabetes, congestive heart failure, and COPD), and 75 percent effective in healthy persons 65 and older. Vaccine effectiveness, however, could not be determined in certain populations of individuals with immunosuppressive conditions.
When PNEUMOVAX23 (PPSV23) was administered in combination with ZOSTAVAX, Merck’s live attenuated shingles vaccine, shingles antibody levels were found to be significantly lower when compared to administering the shingles vaccine four weeks after PNEUMOVAX23 administration.
A 2008 study found that while PPSV23 reduced the risk of invasive pneumococcal disease in the elderly by 38 percent, it had no impact on pneumonia rates. In 2010, researchers found the vaccine to be completely ineffective at reducing the rates of hospitalization or death in persons previously treated for community acquired pneumonia. The vaccine was also found to be ineffective in both transplant patients, and persons with HIV who had low CD4+ cell counts and the vaccine did not reduce the rates of pneumonia in persons with rheumatoid arthritis.
