Socioeconomic Inequalities in Child Immunisation Coverage in Nigeria’s South West Zone: A Secondary Analysis of National Survey Data

Despite gains in national immunisation coverage, significant socioeconomic disparities persist across Nigerian states, with the poorest households and least-educated mothers remaining systematically underserved. This study quantifies socioeconomic inequalities in childhood immunisation coverage in South West Nigeria using secondary analysis of the 2021 Nigeria Demographic and Health Survey (NDHS). Data from 3,184 children aged 12 to 23 months from Ekiti, Lagos, Ogun, Ondo, Osun, and Oyo states were included. Full vaccination coverage was the primary outcome, defined as receipt of BCG, three doses of pentavalent vaccine, three doses of oral polio vaccine, and measles vaccine. Inequality was measured using the Concentration Index (CI), Slope Index of Inequality (SII), and relative concentration curves stratified by wealth quintile and maternal education. Full immunisation coverage was 57.4% in the wealthiest quintile versus 28.1% in the poorest quintile. The Concentration Index for full immunisation was 0.28, indicating pro-rich inequality. Children of mothers with no formal education had a 41.3 percentage point lower coverage than children of mothers with secondary or higher education. Lagos demonstrated the greatest absolute inequality, while Ekiti showed the smallest. Supply-side factors including health worker availability and facility proximity were significant mediators of the inequality gradient. The study recommends equity-focused immunisation strategies targeting the poorest households, community outreach, and demand-side incentive programmes. Keywords: immunisation inequality, socioeconomic, concentration index, South West Nigeria, NDHS.