From district to community: fine-scale data and revised WHO guidance expand schistosomiasis treatment needs in Ethiopia and Zimbabwe

BackgroundSchistosomiasis remains a major public health challenge in sub-Saharan Africa. Recent World Health Organization (WHO) guidance calls for community-wide treatment and fine-scale data to optimise preventive chemotherapy (PC) strategies, yet the practical implications for resource allocation by health ministries are unclear. MethodsWe analysed epidemiological and cost data from Ethiopia and Zimbabwe to compare survey designs and five implementation scenarios. Scenarios varied by data source, administrative unit of implementation, WHO guidance on PC strategies. Outcomes were target population, praziquantel needs, and delivery costs. ResultsGeostatistical surveys reduced sample size by up to 90% and survey costs by [≥]72% compared with a design-based approach, while increasing spatial coverage. Applying updated WHO guidance expanded eligibility to pre-school-aged children and adults, and in one scenario increased treatment needs by 72% in Ethiopia and 262% in Zimbabwe. Correspondingly, praziquantel requirements and delivery costs were driven primarily by expanded age eligibility rather than geographic coverage. ConclusionsGeostatistical surveys provide substantial efficiency gains for impact assessments, enabling cost-efficient, granular targeting. However, implementing 2022 WHO guidance was the dominant driver of increases in programme scope and resource needs, underscoring the importance of accurate fine-scale data to guide efficient planning and budgeting toward elimination goals. Author summarySchistosomiasis control programmes are required to use finer-scale data and updated World Health Organization (WHO) guidance to decide where and how often to deliver praziquantel. We analysed national schistosomiasis data and programme costs from Ethiopia and Zimbabwe to compare different approaches to impact assessment surveys and to estimate how treatment needs change under alternative decision rules.We found that model-based geostatistical surveys can reduce the number of people that need to be sampled and the cost of surveys while providing more detailed information for planning at sub-district level. However, when we applied the 2022 WHO schistosomiasis guidance, expanded eligibility (including adults and pre-school-age children and a lower threshold for community-wide treatment) substantially increased the number of people needing treatment. In our scenarios, expanded eligibility drove much larger increases in praziquantel requirements and delivery costs than changes in geographic coverage. Our findings help health ministries to anticipate the operational and budget implications of updated guidance and highlight why accurate fine-scale data are essential for equitable and realistic planning toward elimination.