Paul TurnerPhana LeabSokeng LySena SaoThyl MiliyaJames D. HeffelfingerNyambat BatmunkhFernanda C. LessaJenny A. WalldorfTerri B. HydeVichit OrkMd Shafiqul HossainKatherine A. GouldJason HindsBen S. CooperChanpheaktra NgounClaudia TurnerNicholas P.J. DayMinistry of Health CambodiaUniversity of LondonOrganisation Mondiale de la SantéCenters for Disease Control and PreventionMahidol UniversitySt George's Hospital, LondonNuffield Department of Clinical MedicineAngkor Hospital for Children2020-06-022020-06-022020-04-10Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. Vol.70, No.8 (2020), 1580-1588153765912-s2.0-85083541311https://repository.li.mahidol.ac.th/handle/123456789/56259© The Author(s) 2019. Published by Oxford University Press for the Infectious Diseases Society of America. BACKGROUND: Cambodia introduced the 13-valent pneumococcal conjugate vaccine (PCV13) in January 2015 using a 3 + 0 dosing schedule and no catch-up campaign. We investigated the effects of this introduction on pneumococcal colonization and invasive disease in children aged <5 years. METHODS: There were 6 colonization surveys done between January 2014 and January 2018 in children attending the outpatient department of a nongovernmental pediatric hospital in Siem Reap. Nasopharyngeal swabs were analyzed by phenotypic and genotypic methods to detect pneumococcal serotypes and antimicrobial resistance. Invasive pneumococcal disease (IPD) data for January 2012-December 2018 were retrieved from hospital databases. Pre-PCV IPD data and pre-/post-PCV colonization data were modelled to estimate vaccine effectiveness (VE). RESULTS: Comparing 2014 with 2016-2018, and using adjusted prevalence ratios, VE estimates for colonization were 16.6% (95% confidence interval [CI] 10.6-21.8) for all pneumococci and 39.2% (95% CI 26.7-46.1) for vaccine serotype (VT) pneumococci. There was a 26.0% (95% CI 17.7-33.0) decrease in multidrug-resistant pneumococcal colonization. The IPD incidence was estimated to have declined by 26.4% (95% CI 14.4-35.8) by 2018, with a decrease of 36.3% (95% CI 23.8-46.9) for VT IPD and an increase of 101.4% (95% CI 62.0-145.4) for non-VT IPD. CONCLUSIONS: Following PCV13 introduction into the Cambodian immunization schedule, there have been declines in VT pneumococcal colonization and disease in children aged <5 years. Modelling of dominant serotype colonization data produced plausible VE estimates.Mahidol UniversityMedicineArticleSCOPUS10.1093/cid/ciz481