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Background. The 23-valent polysaccharide pneumococcal vaccine (PPV) is currently recommended for elderly persons and persons who are at high risk of infection. However, the effectiveness of the 23-valent PPV remains controversial. We assessed the effectiveness of this vaccine in older adults. Methods. A prospective cohort study was conducted from January 2002 through April 2005; it included all community-dwelling individuals aged ⩾65 years who were assigned to 1 of 8 primary health care centers in Tarragona, Spain (11,241 subjects). The primary outcomes were invasive pneumococcal disease, pneumococcal pneumonia, overall pneumonia rate, and death due to pneumonia. All cases were validated by a check of the clinical records. The association between pneumococcal vaccination and the risk of each outcome was evaluated by means of multivariate Cox proportional hazard models, adjusted for age, sex, comorbidity, immunocompetence, and influenza vaccine status. Results. Pneumococcal vaccination was associated with significant reductions in the risk of hospitalization for pneumonia (hazard ratio [HR], 0.74; 95% confidence interval [CI], 0.59–0.92) and in the overall pneumonia rate (HR, 0.79; 95% CI, 0.64–0.98). The incidence of invasive pneumococcal disease was low (64 cases per 100,000 person-years), and a considerable protective effect against invasive pneumococcal disease did not attain statistical significance (HR, 0.60; 95% CI, 0.22–1.65). However, the vaccine showed a significant effectiveness of 45% to prevent pneumococcal pneumonia (HR, 0.55; 95% CI, 0.34–0.88). Finally, vaccination was associated with a significant 59% reduction in the risk of death due to pneumonia among vaccinated subjects (HR, 0.41; 95% Cl, 0.23–0.72) Conclusions. These results indicate that the 23-valent PPV effectively prevented pneumococcal pneumonia (with or without bacteremia) and decreased the rates of overall pneumonia and of mortality due to pneumonia in older adults, providing new arguments for systematic vaccination in the elderly population. [ABSTRACT FROM AUTHOR]