Determinants of geographical inequalities for DTP3 vaccine coverage in sub-Saharan Africa

Childhood immunization is one of the most effective health interventions, making it a key indicator of progress towards universal health coverage. In the last decade, improvements in coverage have been made globally, however, slow progress has been documented in sub-Saharan Africa with considerable subnational variations. We explore potential drivers of equitable immunization services based on subnational DTP3 coverage estimates.Using vaccine coverage at the 5 by 5 km area from 2000 to 2016, we quantify inequality using three measures. We assess the shortfall inequality which is the average deviation across subnational units from that with the highest coverage for each country. Secondly we estimate the threshold index, the proportion of children below a globally set subnational coverage target, and lastly, a Gini coefficient representing the within-country distribution of coverage. We use time series analyses to quantify associations with immunization expenditures controlling for country socio-economic and population characteristics.Development assistance, maternal education and governance were associated with reductions in inequality. Furthermore, high quality governance was associated with a stronger relationship between development assistance and reductions in inequality. Results from this analysis also indicate that countries with the lowest coverage suffer the highest inequalities. We highlight growing inequalities among countries which have met national coverage targets such as South Africa and Kenya. In 2016, values for the shortfall inequality ranged from 1% to 43%, the threshold index from 0% to 100% and Gini coefficient from 0.01 to 0.37. Burundi, Comoros, Eswatini, Lesotho, Namibia, Rwanda, and Sao Tome and Principe had the least shortfall inequality (<5%) while Angola, Ethiopia and Nigeria had values greater than 40%. A similar picture was noted for the other dimensions of inequality among these particular countries.Immunization program investments offer promise in addressing inequality, however, domestic mechanisms for resource implementation and accountability should be strengthened to maximize gains in coverage.