Geospatial Settlement Data and Immunization Reach in Polio SIAs: Evidence from Axis of Intractable Transmission States in Northern Nigeria

Background The persistent transmission of circulating vaccine-derived poliovirus type 2 (cVDPV2) in Northern Nigeria, especially in the Axis of Intractable Transmission (AIT) states, Kebbi, Sokoto, Katsina, and Zamfara, despite national certification of wild poliovirus interruption, is strongly associated with fragmented settlement visibility, population denominator inaccuracies, and uneven implementation of Supplementary Immunization Activities (SIAs). This study examines whether these geospatial investments as broader ecosystem of interventions improve immunization reach and operational quality during cVDPV2 SIAs. Methods A retrospective operational analysis was conducted using data from nine consecutive SIAs (April 2024–June 2025). We extracted state-level indicators from the Master List of Settlements (MLoS) geospatial records and campaign data, which included (1) geospatial completeness, defined as the proportion of settlements with validated coordinates; (2) settlement tracking coverage; (3) MLoS-derived population targets for children; and (4) number of children vaccinated. Descriptive statistics, bivariate exploratory relationships, and temporal learning analysis were performed to evaluate how geospatial status influenced tracking outcomes. Results Geospatial completeness ranged from 92.1% (Zamfara) to 100% (Kebbi) and was associated with higher, more stable tracking coverage. Kebbi, with complete geolocation of settlements, demonstrated consistently strong tracking performance (mean 93%). Settlement tracking correlated positively with vaccination outputs in Kebbi and Sokoto but demonstrated saturation effects in Katsina and diminishing returns in Zamfara. Operational learning was observed in Sokoto, Katsina, and Zamfara, each demonstrating 8 to 10 percentage point improvements in tracking coverage across rounds. Conclusion In addition to other contributory factors, settlement-level geolocation improves the quality and reach of cVDPV2 SIAs by strengthening visibility of target populations and promoting more reliable tracking. The MLoS updates and tracking of settlements and vaccination teams demonstrated transformative potential in optimizing vaccination campaigns by improving equity, accountability, and efficiency. Its deployment offers valuable lessons for enhancing immunization efforts in resource-constrained and security-compromised settings, emphasizing the importance of strategic integration and sustained investments in public health innovation.