Evolving pneumococcal serotypes and sequence types in relation to high antibiotic stress and conditional pneumococcal immunization

In Taiwan, beginning in 2013, the 13-valent pneumococcal conjugate vaccine (PCV13) was provided free of charge to children 2–5 years of age. In 2014, this was extended to children 1–5 years old. During 2012–2014, 953 cases of culture-confirmed pneumococcal disease (CCPD), including 104 invasive pneumococcal disease (IPD), were prospectively identified and analyzed at a 3,700-bed hospital in Taiwan. From 2012 to 2014, the incidence per 10,000 admissions decreased from 26.7 to 20.4 for CCPD (P < 0.001) and from 3.2 to 1.9 for IPD (P < 0.05). Significant reduction of PCV13 serotypes was firstly noted in children in 2013 and extended to both paediatric and adult populations in 2014. Simultaneously, the incidence per 10,000 admissions of non-PCV13 serotypes increased from 6.1 in 2012 to 9.3 in 2014 (P < 0.005). The most prevalent non-PCV13 serotypes were 15A, 15B, and 23A, each containing a predominant clone, ST63(15A), ST83(15B), and ST338(23A). From 2012 to 2014, isolates with penicillin minimum inhibitory concentrations >2 mg/L decreased from 27.8% to 8.1% (P < 0.001) among all isolates. PCV13 immunization in young children demonstrated an early protective effect in all ages. However, in the elderly, the effect was compromised by an emergence of non-PCV13 serotypes.