Assessing Potential Exemplars in Reducing Zero-Dose Children: A Novel Approach for Identifying Positive Outliers in Decreasing National Levels and Geographic Inequalities in Unvaccinated Children

BACKGROUND: Understanding past successes in reaching unvaccinated or "zero-dose" children can help inform strategies for improving childhood immunization in other settings. Drawing from positive outlier methods, we developed a novel approach for identifying potential exemplars in reducing zero-dose children. METHODS: Focusing on 2000-2019, we assessed changes in the percentage of under-one children with no doses of the diphtheria-tetanus-pertussis vaccine (no-DTP) across two geographic dimensions in 56 low- or lower-middle-income countries: (1) national levels; (2) subnational gaps, as defined as the difference between the 5th and 95th percentiles of no-DTP prevalence across second administrative units. Countries with the largest reductions for both metrics were considered positive outliers or potential 'exemplars', demonstrating exception progress in reducing national no-DTP prevalence and subnational inequalities.…