Assessing the Performance of Immunization Services in Sub-Saharan Africa: Timing and Completion Matters

Childhood vaccination coverage globally has increased since the launch of the Expanded Programme on Immunization in 1977 although delayed vaccination and failure to complete the recommended immunization series remains an important obstacle to the control vaccine-preventable disease. In sub-Saharan Africa, where >50% of the world’s preventable deaths under-five years occur, research on the underlying mechanisms of under-vaccination is essential to realizing continued progress in eliminating preventable infectious disease-related morbidity and mortality in infants and young children. This dissertation explores drivers of vaccination disparities in sub-Saharan Africa, focusing on the competing programmatic priorities to innovate with inclusion of new vaccines while also urgently addressing under-vaccination against traditional disease targets. In aim I, we assessed the prevalence of delayed childhood vaccination and its relationship with under-vaccination in the first year of life, pooling Demographic and Health Survey data from 33 sub-Saharan African countries conducted between 2010 and 2018. High prevalence of delayed vaccination (>24%) was found for all doses in the schedule, indicating children were vaccinated >4 weeks after the target age for effective coverage. Delays were strongly associated with incomplete schedules including failure to receive one or more vaccine doses by 12 months of age. In aim 2, we examined the distal relationship between childhood death and immunization utilization patterns among surviving children. Using data from children and their decedent siblings across 33 SSA countries, we found that children with a prior decedent sibling had less favorable vaccination outcomes compared to children who had no prior sibling death. Other measures of child mortality influence were considered at the province-level, which also showed less favorable vaccination outcomes for with surviving children in high U5M strata compared to lower ones. Finally, in aim 3, we evaluated the temporal trends in adherence to age-specific vaccination recommendations in two informal settlement communities in Nairobi, Kenya. In this analysis, we compared trends between defined periods before and after the introduction of new vaccines in the basic immunization schedule using data from the longitudinal Nairobi Urban Health and Demographic Surveillance System between 2007 and 2015. We found no significant differences in the prevalence of delays between the two periods, suggesting no association between the introduction of new vaccines and the timeliness of delivering subsequent routine immunizations. Together, this dissertation examined perspectives not previously considered on how underlying mechanisms inherent to immunization program delivery and prioritization influence overall progress towards aspirational goals for achieving effective coverage. By combining multiple measures, these studies contribute new ways of monitoring the performance of immunization programs in low coverage countries and informing the design of strategies to improve coverage in order to expand protection against vaccine-preventable diseases to all children.