Distribution and annual changes in the proportion of Streptococcus pneumoniae serotypes in Japanese adults with pneumococcal pneumonia from 2011 to 2017.

In 2014, vaccinations with 23-valent pneumococcal polysaccharide vaccine (PPSV23) and 13-valent pneumococcal conjugate vaccine (PCV13) were implemented in Japan for all adults aged ≥65 years. We previously clarified reductions in the proportions of PCV7-, PCV13-, and PPSV23-covered serotypes in patients with pneumococcal pneumonia after the initiation of PCV7 and PCV13 vaccinations for Japanese children; however, information about the annual changes in the proportion of Streptococcus pneumoniae serotypes in patients with pneumococcal pneumonia after the initiation of routine PPSV23 vaccinations remains unclear. We retrospectively studied 229 adults with pneumococcal pneumonia which S. pneumoniae was cultured from their lower respiratory tract samples between 2011 and 2017 and investigated the annual changes in the proportion of S. pneumoniae serotypes. The proportion of PPSV23-covered serotypes decreased from 71.4% in 2011 to 52.2% in 2014, but it remained essentially unchanged from 2015 to 2017. The proportions of PCV7-covered serotypes decreased from 46.4% in 2011 to 4.3% in 2014; however, this rate increased beginning in 2015 and reached 20.6% in 2017. Among the PCV7-covered serotypes, the proportion of the 19F serotype increased from 2015 to 2017. In conclusion, there were no obvious changes in the proportion of PPSV23-covered and PCV13-covered serotypes in patients with pneumococcal pneumonia after the initiation of routine PPSV23 vaccinations.