Background The effectiveness of the 23-valent pneumococcal polysaccharide vaccine (PPSV23) in preventing pneumococcal pneumonia has been controversial. Methods To evaluate the effectiveness of the PPSV23 in elderly outpatients with chronic respiratory diseases, we carried out a case–control study, including 4128 outpatients aged ≥ 65 years, in the respiratory department. Results There were 320 vaccinated patients, of which 164 were diagnosed with pneumococcal pneumonia. The adjusted odds ratio was 0.39 (95% confidence interval (CI), 0.17 to 0.89). In the subsets consisting of age groups ≥ 70 and ≥ 75 years, the adjusted odds ratio (95% CI) was respectively 0.16 (0.04 to 0.67) and 0.15 (0.02 to 1.12). Conclusion This real-world study suggests that PPSV23 can be useful in preventing pneumococcal pneumonia in the elderly with chronic respiratory diseases.

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