CONTEXT. Pneumococcal conjugate bacterial vaccines that are able to prevent invasive disease and mucosal infections have been developed. OBJECTIVE. A meta-analysis of published data from trials on pneumococcal conjugate vaccine was performed to determine the efficacy in reducing the incidence of invasive disease caused by Streptococcus pneumoniae, pneumonia, and acute otitis media in healthy infants younger than 24 months. METHODS. A systematic search of the literature was conducted. Controlled clinical trials had to compare the protective efficacy of the pneumococcal conjugate vaccine in reducing the incidence of invasive disease caused by S pneumoniae, pneumonia, and acute otitis media in healthy infants with placebo or control vaccines. Information was extracted by using a standardized protocol. RESULTS. The efficacy of pneumococcal conjugate vaccine in the reduction of invasive pneumococcal disease was 89% involving vaccine serotypes in both the intention-to-treat and per-protocol analyses and ranged from 63% to 74% for all serotypes. The efficacy to prevent acute otitis media sustained by vaccine serotypes was 55% in the intention-to-treat and 57% in the per-protocol analyses, whereas it was 29% to prevent otitis involving all serotypes in the per-protocol analysis. Finally, in the intention-to-treat and per-protocol analyses, the efficacy to prevent clinical pneumonia was 6% and 7%, respectively, whereas for the prevention of radiograph-confirmed pneumonia it was 29% and 32%, respectively. CONCLUSIONS. The pneumococcal conjugate vaccine produces a significant effect regarding prevention of invasive pneumococcal disease. Results on prevention of otitis or pneumonia have been less striking, but considering the high burden of these diseases in infants, even a low efficacy has potential for tremendous impact on the health of infants in developing and industrialized countries.