Background The serotype-specific effectiveness of 23-valent pneumococcal polysaccharide vaccine (PPV23) against pneumococcal pneumonia has not been established in people aged 65 years or older. We assessed the effectiveness of PPV23 in this population.
Methods For this multicentre, prospective study, we enrolled all individuals aged 65 years or older with community-onset pneumonia who visited four study hospitals in Japan between Sept 28,2011, and Aug 23,2014. Streptococcus pneumoniae was isolated from sputum and blood samples, and serotyped by the capsular Quellung method. Sputum samples were further tested by PCR assay to identify pneumococcal DNA, and positive samples were examined for 50 serotypes by a nanofluidic real-time PCR assay. Urine samples were tested by a urinary antigen test. Serotype-specific vaccine effectiveness was estimated using the test-negative design.
Findings 2621 eligible patients visited the study hospitals, of whom 585 did not have sputum samples available and were excluded from our analysis. 419 (21%) of 2036 patients were positive for pneumococcal infection (232 by sputum culture, 317 by sputum PCR, 197 by urinary antigen test, and 14 by blood culture). 522 (26%) patients were judged to be vaccinated in the analyses. Effectiveness of PPV23 was 27.4% (95% CI 3.2 to 45.6) against all pneumococcal pneumonia, 33.5% (5.6 to 53.1) against PPV23 serotypes, and 2.0% (-78.9 to 46.3) against non-PPV23 serotypes. Although no significant differences between subgroups were seen, higher protection was noted in people younger than 75 years, women, and individuals with lobar pneumonia or health-care-associated pneumonia.
Interpretation PPV23 showed low to moderate effectiveness against vaccine serotype pneumococcal pneumonia in people aged 65 years or older. To improve the current pneumococcal vaccination programme, the variability of PPV23 effectiveness in different groups of older people must be further investigated.