Serotype Replacement in Adult Pneumococcal Pneumonia after the Introduction of Seven-Valent Pneumococcal Conjugate Vaccines for Children in Japan: a Systematic Literature Review and Pooled Data Analysis

Streptococcus pneumoniae is the major causative agent for adult pneumonia. Following the introduction of pneumococcal conjugate vaccines (PCV) for children, serotype replacement has been reported in adult invasive pneumococcal diseases but has not been well studied for cases of pneumococcal pneumonia in adults in Asia. To investigate serotype replacement in adult pneumococcal pneumonia in Japan, we conducted a systematic review of the literature across 5 databases using terms, including pneumococcus, serotype, their synonyms, and derivatives. After the assessment of the identified articles, data on the pneumococcal serotype distribution among adult pneumonia cases were extracted from relevant studies. Twenty-two studies were reviewed, and 4 relevant articles were included in the pooled data analysis. The proportion of the 7-valent PCV (PCV7)-covered serotypes from before and after the introduction of PCV7 for children (-18.1%, p < 0.001) significantly decreased; moreover, the proportions of serotypes covered by PCV13 but not PCV7 (+ 9.9%, p = 0.003) and those covered by the 23-valent polysaccharide vaccine but not PCV7 (+ 9.4%, p = 0.007) significantly increased. Serotype replacement occurred in adult cases of pneumococcal pneumonia following vaccination of children with PCV7 in Japan. Further nationwide surveillance is warranted to investigate serotype replacement in the post-PCV13 phase.