The distribution and annual changes in the Streptococcus pneumoniae serotypes in adult Japanese patients with pneumococcal pneumonia from 2011 to 2015

[[[ Background: ]]] We previously reported a decrease in the vaccine serotypes of a 7-valent pneumococcal conjugate vaccine (PCV7) and pneumococcal polysaccharide vaccine (PPSV) 23 in adult pneumonia patients after starting PCV7 vaccination in children in Japan between 2011 and 2013, suggesting that the vaccination of children had an indirect effect on adults. PCV7 was replaced by PCV13 in 2013 and was authorized for individuals ≥65 in 2014; vaccination with PPSV23 has been routinely implemented since the same year. We continuously evaluated the pneumococcal serotype changes. [[[ Methods: ]]] This retrospective epidemiological study was performed at the University of Occupational and Environmental Health, Japan, from January 2014 to December 2015, while also referring to the data from January 2011 to December 2013. The pneumococcal serotypes that were isolated from pneumonia patients and clinical information were evaluated. [[[ Results: ]]] The proportions of the PCV7 and PCV13 vaccine serotypes significantly decreased each year (from 2011 to 2015) from 46.4% to 8.3% (p < 0.05) and 71.4% to 33.3% (p < 0.05), respectively. The PPSV23 serotypes without PCV13 showed a continuous, mild increase, while the mortality rates tended to decrease in patients with pneumococcal pneumonia. [[[ Discussion: ]]] The present study showed that the vaccine serotypes of PCV7 and PCV13 have been decreasing since the introduction of PCV7 in October 2009 and since PCV13 was introduced to replace PCV7 from November 2013, and that the mortality rates of patients have tended to decrease. These results indicate that a continuous analysis of the pneumococcal serotype data is necessary for the appropriate administration of vaccines.