Impact of 13-Valent Pneumococcal Conjugate Vaccine on Colonization and Invasive Disease in Cambodian Children

Abstract

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.

Keywords: Streptococcus pneumoniae; Cambodia; children; colonization; vaccine.

Figure 1.

Pneumococcal colonization, stratified by age category, pneumococcal serotype category, and time period. Results for 2014 are the combined data from January and August surveys. Abbreviations: NT, nontypeable; NVT, nonvaccine type; PCV, pneumococcal conjugate vaccine; VT, vaccine type.

Figure 2.

Pneumococcal serotype colonization, by proportion of total isolates in each time period. Light gray lines show detected serotypes as a proportion of all isolates from that year, with a single serotype highlighted in color (green = vaccine type; blue = nonvaccine type; red = nontypeable [NT]). The vertical black dashed line represents 13-valent pneumococcal conjugate vaccine introduction.

Figure 3.

Observed and modeled IPD IRRs for the late post-PCV (2018) and pre-PCV (2012–2014) time periods. For clarity, the upper bound of the confidence interval for the observed NVT IRR has been truncated at 8 (actual value 15.6). The dashed horizontal line indicates an IRR of 1. Abbreviations: CI, confidence interval; IPD, invasive pneumococcal disease; IRR, incidence rate ratio; NVT, nonvaccine type; PCV, pneumococcal conjugate vaccine; VT, vaccine type.