UCLA

Poliovirus, once a global pandemic is now in its endgame eradication stages. Currently, wild poliovirus type 2 and 3 have been declared eradicated by the World Health Organization (WHO) and wild type 1 is circulating in just two remaining countries. As the Sabin oral polio vaccine utilizes a live attenuated strain of poliovirus, in 2012 the WHO General Assembly released a strategic plan for polio eradication that called for the eventual removal of the oral polio vaccine. In April 2016, the WHO coordinated a global switch day where trivalent oral polio vaccines containing poliovirus type 2 were replaced with bivalent vaccines containing polio types 1 and 3 only. Since then, vaccine-derived poliovirus infections in the Democratic Republic of the Congo (DRC) have risen as polio vaccine coverage rates, and specifically rates against serotype 2, have fallen. This dissertation serves to contribute towards polio eradication efforts in the DRC by describing the landscape of childhood vaccination against poliovirus in a vaccine-derived poliovirus endemic region and quantify how the key vaccine intervention, supplementary immunization campaigns, contribute to improving vaccine coverage. Chapter 1 provides a summary of the pathology of polio and its pandemic history, as well as the WHO endgame strategic plan and policies and the landscape of polio in DRC. Chapter 2 quantifies community immunity against poliovirus and risk factors for under immunization among children under five in an outbreak prone region of southeastern DRC. Chapter 3 explores how repeated immunization interventions impacts community vaccine coverage and uses propensity score weighting to compare a gold standard biomarker for vaccination to material recall collected via questionnaire. Chapter 4 explores the spatial point process of vaccine-derived poliovirus cases and how spatial access to health care can impact under-vaccination. This dissertation finds that ultimately, access to vaccine in the DRC is an enduring issue related to challenges associated with DRC’s resource-poor health system and systemic issues with infrastructure. Vaccine immunization campaigns do improve community immunity, but likely are not providing adequate coverage to halt the spread of vaccine-derived polio viruses. Addressing the limitations of the current vaccine strategy head on can help move the DRC closer to polio eradication.