Carriage of Streptococcus Pneumoniae In Unvaccinated Toddlers At The Time of Pneumococcal Conjugate Vaccine Implementation Into The National Immunization Program In Poland

Abstract We investigated pneumococcal carriage among unvaccinated children under five years of age at the time of conjugate polysaccharide vaccine (PCV) introduction into the national immunization program (NIP). Paired nasopharyngeal swab (NPS) and saliva samples collected between 2016 and 2020 from n=394 children were tested with conventional culture and using qPCR. The carriage rate detected by culture was 25.4% (97 of 394), by qPCR 39.1% (155 of 394), and 40.1% (158 of 394) overall. The risk of carriage was significantly elevated among day care center attendees, and during autumn/winter months. Among strains cultured, the most common serotypes were: 23A, 6B, 15BC, 10A, 11A. The coverage of PCV10 and PCV13 was 23.2% (23 of 99) and 26.3% (26 of 99), respectively. Application of qPCR lead to detection of 168 serotype carriage events, with serogroups 15, 6, 9 and serotype 23A most commonly detected. Although the highest number of carriers was identified by testing NPS with qPCR, saliva significantly contributed to the overall number of detected carriers. Co-carriage of multiple serotypes was detected in 25.3% (40 of 158) of carriers. Results of this study represent a baseline for the future surveillance of effects of pneumococcal vaccines in NIP in Poland.