Mapping the Unvaccinated: Why 13.5 Million Zero-Dose Children Remain Hard to Find

A review of 102 studies across 68 low- and lower-middle-income countries finds that geospatial tools are mostly applied to routine immunisation coverage rather than to the 13.5 million children who have never received a vaccine. Researchers point to survey gaps, thin evidence in high-burden countries and a need for better routine data.