Multivariate assessment of vaccine equity in Nigeria: A VERSE tool case study using demographic and health survey 2018

Nigeria experiences wide heterogeneity in vaccination rates by vaccine and region. However, inequities in vaccination status extend beyond just geographic covariates. Traditionally, inequity is represented by a single metric pertaining to socioeconomic status. A growing body of literature suggests that this view is limiting, and a multi-factor approach is necessary to comprehensively evaluate relative disadvantage between individuals. The Vaccine Economics Research for Sustainability and Equity (VERSE) tool produces a composite equity metric, which accounts for multiple factors influencing inequity in vaccination coverage. We apply the VERSE tool to Nigeria's 2018 Demographic and Health Survey (DHS) to cross-sectionally evaluate equity in vaccination status for national immunization program (NIP) vaccines over the following contributing covariates: age of child, sex of child, maternal education level, socioeconomic status, health insurance status, state of residence, and urban or rural designation. We also assess equity for zero-dose, fully immunized for age, and completion of NIP. Results show that socioeconomic status contributes substantially to variation vaccination coverage, but it is not the most substantial factor. For all vaccination statuses, except for NIP completion, maternal education level is the greatest contributor towards a child's immunization status among model variables. We highlight the outputs for zero-dose, fully immunized at infancy, MCV1 and PENTA1. The percentage point gap in vaccination status between the top and bottom quintiles of disadvantage, as ranked by the composite indicator is 31.1 (29.5–32.7) for zero-dose status, 53.1 (51.3–54.9) for full immunization status, 48.9 (46.9–50.9) for MCV1, and 67.6 (66.0–69.2) for PENTA1. Though concentration indices indicate inequity for all statuses, full immunization coverage is very low at 31.5% suggesting significant gaps in reaching children after initial doses for routine immunizations. Applying the VERSE tool to future Nigeria DHS surveys can allow decisionmakers to track changes in vaccination coverage equity, in a standardized manner, over time.