Epidemiology of hospitalized paediatric community-acquired pneumonia and bacterial pneumonia following the introduction of 13-valent pneumococcal conjugate vaccine in the national immunization programme in Japan

Studies on community-acquired pneumonia (CAP) and pneumococcal pneumonia (PP) related to 13-valent pneumococcal conjugate vaccine (PCV13) introduction in Asia are scarce. This study aimed to investigate the epidemiological and microbiological determinants of hospitalized CAP and PP after PCV13 was introduced in Japan. This observational hospital-based surveillance study included children aged ≤15 years, admitted to hospitals around Chiba City, Japan. Participants had bacterial pneumonia based on a positive blood or sputum culture for bacterial pathogens. Serotype and antibiotic-susceptibility testing of Streptococcus pneumoniae and Haemophilus influenzae isolates from patients with bacterial pneumonia were assessed. The CAP hospitalization rate per 1000 child years was 17.7, 14.3, and 9.7 in children aged <5 years and 1.18, 2.64, and 0.69 in children aged 5 15 years in 2008, 2012, and 2018, respectively. There was a 45% and 41% reduction in CAP hospitalization rates, between the pre-PCV7 and PCV13 periods, respectively. Significant reductions occurred in the proportion of CAP due to PP and PCV13 serotypes. Conversely, no change occurred in the proportion of CAP caused by H. influenzae. The incidence of hospitalized CAP in children aged ≤15 years was significantly reduced after the introduction of PCV13 in Japan. Continuous surveillance is necessary to detect emerging PP serotypes.