Pneumococcal Serotypes in Urban Ugandan Children Vaccinated with the 10-Valent Pneumococcal Conjugate Vaccine

Abstract Objective Uganda introduced the 10-valent pneumococcal conjugate vaccine (PCV10) into routine infant immunization in 2014, but post-introduction molecular data on residual vaccine-type carriage remain limited. We assessed nasopharyngeal pneumococcal carriage and vaccine-type serotype distribution among urban Ugandan children aged ≤ 5 years, five years after PCV10 introduction, using real-time quantitative PCR (RT-qPCR). Results In this cross-sectional follow-up study, 156 stored nasopharyngeal bacterial isolates from 196 children were re-cultured and re-characterized; 64/90 phenotypically identified pneumococcal isolates were confirmed by lytA RT-qPCR, corresponding to an overall pneumococcal carriage prevalence of 33% (64/195). Molecular serotyping of all 64 pneumococcal isolates for PCV10/PCV13-associated capsular targets identified 23/64 (35.9%) vaccine-type isolates, while 41/64 (64.1%) were non-vaccine or non-typeable by the assay panel. Serotype 14 predominated (6/64, 9.4%), followed by 19A (5/64, 7.8%), and serotypes 3, 7F, and 9V (each 4/64, 6.3%); serotype 18C was detected in 1/64 (1.6%). Serotypes 1, 4, 5, 6A/6B, 19F, and 23F were not detected. Persistent carriage of PCV10 serotypes 7F, 9V, 14, and 18C indicates residual vaccine-type circulation despite an overall reduction in carriage prevalence. This is concerning, since a low universal carriage prevalence is necessary for effective pneumococcal disease control.