Changes in the features of invasive pneumococcal disease after introduction of the seven-valent pneumococcal conjugate vaccine in a regional core hospital of Kochi, Japan

Since the introduction of the seven-valent pneumococcal conjugate vaccine (PCV7) in 2007, invasive pneumococcal disease has declined, but the incidence of Streptococcus pneumoniae serotype 19A has risen worldwide. The present study examined changes in the features of invasive pneumococcal disease since the introduction of the PCV7 in Kochi, Japan. Pediatric cases of invasive pneumococcal disease were investigated before and after vaccine introduction (January 2008 to December 2013). Cases of invasive pneumococcal disease tended to decrease after PCV7 introduction. In addition, before introduction of the vaccine, most serotypes causing invasive pneumococcal disease were those included in the vaccine. However, after the introduction, we found cases infected by serotypes not covered by vaccine. Penicillin-resistant S. pneumoniae was the predominant serotype causing invasive pneumococcal disease before introduction of the PCV7, and the susceptibility of this serotype to antibiotics improved after vaccine introduction. Serotype isolates identified after vaccine introduction were also relatively susceptible to antibiotic therapy, but decreased susceptibility is expected.