Abstract

BACKGROUND: Following programmatic introduction of the 13-valent pneumococcal conjugate vaccine (PCV13), there is residual carriage and disease due to PCV13 covered serotypes. METHODS: 988 PCV13-immunised children aged 13-48 months were enrolled between February 2014 and August 2015 (late-PCV13), and had nasopharyngeal pneumococcal carriage compared with 567 PCV7-immunised children enrolled into a study 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. Blood collected from the late-PCV13 cohort was assessed for levels of serotype-specific serum IgG by multiplex immunoassay. RESULTS: Compared with PCV7-immunised children, carriage among PCV13-immunised children was significantly lower for serotypes 19A (OR=0.08, 95% CI 0.02-0.25), 6C (OR=0.11, 95% CI 0.03-0.32) and 7F (8 vs 0 cases).IPD incidence in children <5 years was significantly lower for serotypes 1 (IRR=0.03, 95% CI 0-0.19) and 7F (IRR=0.13, 95% CI 0.05-0.36) but not 19A (IRR=0.6, 95% CI 0.3-1.12) or serotype 3 (IRR=2.3, 95% CI 0.86-6.15) 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.Children from the late-PCV13 period, who had serum analysed, and were not carrying a PCV13 serotype, had high levels of antibody presumed to be due to natural exposure, to serotypes 3 (24/204, 11.76%) and 19A (14/204, 6.86%). CONCLUSIONS: PCV13 has reduced serotype 19A carriage among vaccinated children however, disease is not fully controlled. We also found, no impact of PCV13 on serotype 3 carriage or disease, and emergence of non-PCV13 serotype disease.