High-Resolution Mapping of DTP1-3 and MCV1 Immunization Coverage and Estimates of Zero-Dose and Under-Vaccinated Children in the Democratic Republic of the Congo

Background/Objectives: Immunization coverage in the Democratic Republic of the Congo (DRC) consistently falls short of global standards, placing the country among those with the highest prevalence of unvaccinated or "zero-dose" children. This study aimed to generate high-resolution (1 km × 1 km) geospatial estimates of coverage for the first to third doses of diphtheria-tetanus-pertussis vaccine (DTP1-3) and the first dose of measles-containing vaccine (MCV1), along with estimates of zero-dose and under-vaccinated children to support vaccination programming in DRC. Methods: We used Bayesian geostatistical modelling to integrate data from the 2023 Enquête de Couverture Vaccinale (ECV) survey with geospatial covariates and harmonized population datasets. The model generated vaccine coverage and dropout rates at 1 × 1 km resolution while accounting for spatial dependence and prediction uncertainty. Grid-level estimates were aggregated to health areas, health zones, and provinces using population-weighted averages, and combined with under-one population estimates to quantify zero-dose and DTP-under-vaccinated children. Results: The grid-level unconstrained coverage estimates (estimation over all land grid squares) showed substantial variability across the country (DTP1: 13.3 to 99.7%; DTP2: 12.3 to 96.8%; DTP3: 3.1 to 93.6%; and MCV1: 7.5 to 93.6%). In total, 56.4% of mapped health areas achieved DTP1 coverage above 80%, but this declined to 32% for DTP2, 15% for DTP3, and 8.3% for MCV1. Around 60.5% of the health zones achieved DTP1 coverage ≥ 80%, while only 2.7% fell below 40%, indicating that substantial disparities persist across these zones. Nationally, based on constrained coverage estimates (only areas with identified built settlements) applied to an estimated 4.2 million children under 1 year in 2024, 18.4% had not received DTP1, 20.7% were DTP-under-vaccinated (received DTP1 but not DTP3), and 46.8% remained unvaccinated for MCV1. Conclusions: The prevalence of large numbers of zero-dose children, together with increased dropout rates, underscores systemic issues in access and follow-up initiatives. These findings are critical for microplanning and targeted outreach to achieve equitable immunization coverage in line with the Immunization Agenda 2030's goal of leaving no child behind.