Heptavalent pneumococcal conjugate vaccine (PCV7) was introduced to Japan in 2010. We investigated the impact of PCV7 on childhood community-acquired pneumonia (CAP) and pneumococcal pneumonia (PP). Children aged <5 years living in Chiba city, Japan, who were admitted to hospitals were enrolled to estimate the incidence of CAP based on the mid-year population. PP was determined by the presence of Streptococcus pneumoniae in cultured blood and/or sputum samples of CAP patients. The incidence of CAP and S. pneumoniae isolated from PP patients was compared before (April 2008-March 2009) and after (April 2012-March 2013) the introduction of PCV7 immunization. The annual incidence of CAP was reduced [incidence rate ratio 0·81, 95% confidence interval (CI) 0·73-0·90]. When comparing post-vaccine with pre-vaccine periods, the odds ratio for PP incidence was 0·60 (95% CI 0·39-0·93, P = 0·024). PCV7-covered serotypes markedly decreased (66·6% in pre-vaccine vs. 15·6% in post-vaccine, P < 0·01), and serotypes 6C, 15A, 15C and 19A increased. Multidrug-resistant international clones in the pre-vaccine period (Spain6B-2/ST90, Taiwan19F-14/ST236) decreased, while Sweden15A-25/ST63 was the dominant clone in the post-vaccine period. A significant reduction in the incidence of both CAP hospitalizations and culture-confirmed PP of vaccine serotypes was observed at 2 years after PCV7 vaccination.
Keywords: Antibiotic resistance; Streptococcus pneumoniae (pneumococcus); community-acquired pneumonia; immunization (vaccination); infectious disease epidemiology.