A Cochrane review included 25 trials: 18 RCTs with 64 852 participants and 7 non-RCTs with 62 294 participants. The studies were conducted among diverse populations, who were either with or without underlying elevated risk of pneumococcal disease due to underlying medical illnesses or environmental factors. A majority of participants were 65 years or older. Pneumococcal polysaccharide vaccines (PPV) reduced invasive pneumococcal disease (IPD) (OR 0.26, 95% CI 0.14 to 0.45). There was efficacy against all-cause pneumonia in low-income (OR 0.54, 95% CI 0.43 to 0.67, I²=19%) but not high-income countries in either the general population (OR 0.71, 95% CI 0.45 to 1.12, I²=93%) or in adults with chronic illness (OR 0.93, 95% CI 0.73 to 1.19, I²=10%). PPV was not associated with reductions in all-cause mortality (OR 0.90, 95% CI 0.74 to 1.09). Vaccine efficacy appeared poorer in adults with chronic illness. Non-RCTs provided evidence for protection against IPD in populations for whom the vaccine is currently utilised (OR 0.48, 95% CI 0.37 to 0.61).