Abstract
Streptococcus pneumoniae is a leading cause of community-acquired pneumonia (CAP) in adults. With the introduction of pneumococcal conjugate vaccines (PCVs) into pediatric national immunization programs, the serotype distribution of pneumococcal disease among adults has changed due to indirect effect. In Japan, PCV15 and PCV20 have been introduced, and PCV21 is under review for approval in adults. This multicenter observational study assessed pneumococcal serotypes in 583 adult patients with community-acquired, culture-positive pneumococcal pneumonia from May 2019 to December 2022. Pneumococcal isolates were serotyped using the Quellung reaction. The median patient age was 74 years (interquartile range: 66-82 years), 383 (65.7%) patients were male, 387 (66.4%) patients had one or more underlying medical conditions, 425 patients (72.9%) were hospitalized, and 305 (52.3%) had a CURB-65 score ≥2. The most common serotypes were serotype 3 (12.5%), 35B (12.0%), 15A (7.7%), 11A (6.7%), and 23A (6.3%). The proportion of serotypes covered by PCV13, PCV15, PCV20, PPSV23, and PCV21 were 24.0, 28.0, 43.7, 44.1, and 71.9%, respectively. The proportions of vaccine-covered serotypes were similar between patients aged <65 and ≥65 years. Serotype 3 was more prevalent among patients living in nursing homes (25.9%) compared with those living at home (11.2%). The proportions of PCV20- and PCV21-covered serotypes suggest that these new vaccines may offer additional protection against adult pneumococcal pneumonia. Given the availability of newly developed PCVs for adults in Japan, reassessing the optimal pneumococcal vaccination policy for adults is warranted.