Estimating the True Population at Risk: Under-Five Malaria Mortality, Denominator Uncertainty, and Child Survival Investment Priorities in Zamfara State, Nigeria

Malaria remains a leading cause of mortality among children under five years of age in Nigeria, yet uncertainty in target population estimates and the coexistence of multiple child health vulnerabilities limit the effectiveness of intervention planning. This study developed a geospatial framework to quantify underfive malaria mortality rates, evaluate denominator uncertainty, and identify child survival investment priorities across Zamfara State, Nigeria. Monthly LGA-level underfive malaria deaths from 2014–2024, household microcensus data, the WorldPop 2025 underfive population raster, malaria burden indicators, immunization coverage, and healthcare access metrics were integrated within a geographic information system. Annual underfive malaria deaths increased from 221 in 2014 to 706 in 2024, with a mean annual burden of 334 deaths. The number of predicted deaths from underfive malaria cases for 2025 ranged from fewer than 10 cases to 129 deaths, with Gusau, Talata Mafara, Gummi, Maru, and Kaura Namoda exhibiting the highest mortality burdens. The household-enumerated and raster-derived underfive populations numbered 838,969 and 848,590, respectively, differing by 9,621 children (1.15%) at the state level; however, the LGA-level discrepancies ranged from –55.4% to +54.5%, with a mean absolute difference of 25.1%. The Child Survival Gap Index identified Gusau, Talata Mafara, Maru, Bungudu, and Kaura Namoda as priority LGAs where high malaria mortality, treatment gaps, immunization deprivation, weak healthcare access, and denominator uncertainty converge. These findings provide an evidence-based framework for geographically targeted malaria and child health interventions in resource-constrained settings.