Childhood Vaccines in Uganda and Zambia: Determinants and Barriers to Effective Coverage

Abstract

As a target of the Sustainable Development Goals, improving childhood immunization is a major priority for global health. Despite progress in recent times however, coverage (vaccination) and effective coverage (immunity) remain a challenge in low and middle-income countries (LMICs). Policy makers, public health practitioners and global organizations such as Gavi, the Vaccine Alliance focus much of their efforts on removing the barriers that prevent children from successful immunization. Barriers to effective coverage are complex and difficult to measure though. Extensive research effort has been devoted to understanding them, but most studies and systematic reviews have been limited in bread and depth. As vaccine programs in LMICs continue progress toward effective coverage of immunizations, better understanding of determinants and barriers will be imperative to close remaining gaps and inequities. Policies and programs like Gavi's health system strengthening support would benefit from a more rigorous examination of the determinants and barriers to immunization. The work presented here represents a small step towards better understanding of why some children remain unvaccinated, and why some vaccines fail to produce immunity. The approach, from the onset, was intended to be more integrated than conventional research. It begins with a systematic review, seeking to uncover the entire body of evidence on determinants to vaccination and immunization. Qualitative research methods were employed to synthesize that systematic review into a testable hypothesis. Using innovative survey data, that hypothesis is immediately put to use to measure key determinants quantitatively in Uganda and Zambia. To bolster the results, a novel data processing method was developed that enhances the accuracy and utility of serological data. Finally, this study presents the results of a Bayesian structural equation model that represents determinants of vaccine coverage, and explores the implications of the findings. The key findings give a rigorous, quantitative account that determinants of effective coverage are different depending on context. In Uganda and Zambia, the results show that there is a set of barriers to whether or not a child receives their initial dose of a vaccine, and those are largely different than the barriers to completion of the full dosage schedule. Further still, the challenges associated with newly-introduced vaccines such as pneumococcal conjugate vaccine are different than either initiation or drop-out. More specifically, this analysis finds that access-related barriers are key to vaccine initiation, demand-related determinants are key to drop-out, and supply-side constraints are key to new vaccines. There are two important implications of these results. First, programs that seek the intervene on a particular barrier, such as demand generation activities or health system strengthening, can use this study to identify the most appropriate outcome to measure their performance. More importantly, vaccination programs in Uganda and Zambia can use these findings to better target new interventions, and continue progress against vaccine preventable diseases.