Impact of pneumococcal conjugate vaccine in children on the serotypic epidemiology of adult invasive pneumococcal diseases in Taiwan

Background: Invasive pneumococcal disease (IPD) causes significant morbidity and mortality, especially in children and older adults. Pneumococcal 7-valent and 13-valent conjugate vaccines (PCV7 and PCV13) were introduced in Taiwan in 2005 and 2011, respectively, for children. This study was conducted to evaluate the impact of PCV administered in children on adult IPD. Methods: From the logbooks of microbiology laboratories, we retrospectively retrieved Streptococcus pneumoniae isolates, collected from normally sterile sites in adult patients. One hundred and fifty-seven consecutive, nonduplicated isolates were collected from one hospital during 2001 and 2003 (pre-PCV period) and 150 isolates from three hospitals from July 2011 to June 2015 (post-PCV period). Serotypes were determined by Quellung test. Results: Among the 307 isolates, 31 serotypes/serogroups were identified. PCV7 serotypes, particularly types 14 (31.2%), 23F (19.7%) and 6B (12.7%) dominated in the pre-PCV period (78.3%) but significantly decreased in the post-PCV period (36%) (p < 0.01). PCV13 specific serotypes (PCV13–PCV7) significantly increased from 7% of the isolates in the pre-PCV period to 28.7% of the isolates in the post-PCV period (p < 0.001), particularly type 19A (from 0.6% to 10%) and 6A (from 0 to 6.7%). Serotype 15B also increased significantly from 0.6% to 6.7% (p < 0.01). Nonvaccine serotypes increased significantly in the post-PCV period (11.5% to 22.0%, p < 0.05), particularly type 15A (from 0 to 4.4%, p < 0.01). Conclusion: Serotype distribution of adult IPD in Taiwan has evolved after the introduction of PCV in children, indicating an indirect impact in adults. Continuous surveillance after the PCV13 vaccination program in children is needed