Persistent Circulation of Vaccine Serotypes and Serotype Replacement After 5 Years of Infant Immunization With 13-Valent Pneumococcal Conjugate Vaccine in the United Kingdom

Background. Following programmatic introduction of the 13-valent pneumococcal conjugate vaccine (PCV13), there is residual carriage and disease due to PCV13-covered serotypes. Methods. PCV13-immunized children aged 13-48 months, N = 988, were enrolled between February 2014 and August 2015 ("late PCV13"), and had nasopharyngcal pneumococcal carriage compared with 7-valent pncumococcal conjugate vaccine (PCV7) immunized children, N = 567, enrolled between November 2010 and September 2011 ("early PCV13"). Nasopharyngeal pneumococci were molecular-serotyped by microarray. Invasive pneumococcal disease (IPD) cases were identified through enhanced national surveillance. Results. Compared with PCV7-immunized children, carriage among PCV13-immunized children was significantly lower for serotypes 19A (odds ratio [OR], 0.08 [95% confidence interval {Cl}, .02-.25]), 6C (OR, 0.11 [95% CI, .03-.32]), and 7F (8 vs 0 cases). IPD incidence in children <5 years was significantly lower for serotypes 1 (incidence rate ratio [IRR], 0.03 [95% CI, 0-.19]) and 7F (IRR, 0.13 [95% CI, .05-.36]) but not 19A (IRR, 0.6 [95% CI, .3-1.12]) or serotype 3 (IRR, 2.3 [95% CI, .86-6.15]) in the late PCV13 period than in the early PCV13 period. 'the most significant rises in IPD incidence were for serotypes 8, 12F, and 24F. Conclusions. PCV13 has reduced serotype 19A carriage among vaccinated children. We found no impact of PCV13 on serotype 3 carriage or disease, and emergence of non-PCV13-serotype disease.