Age-group visibility in WHO schistosomiasis reporting: decomposing preventive-chemotherapy coverage indicators, 2014–2024

Background Age-inclusive schistosomiasis policy requires monitoring that distinguishes between eligible age groups. The 2022 World Health Organization (WHO) guideline recommended treatment from 2 years of age in qualifying communities. We examined what public reporting makes visible for adults and school-age children (SAC), distinguishing information availability from programme scope and treatment receipt. Methods We analysed all 567 country-year records from 52 countries during the 2014–2024 window in a frozen WHO schistosomiasis Preventive Chemotherapy and Transmission Control databank snapshot. Counts of adults requiring treatment and adults reported as treated were derived using a source-specific contract for interpreting age fields. Population-weighted adult and SAC reported-coverage indicators were each decomposed into a reporting-denominator share and conditional reported coverage. We audited missingness states, count anomalies, and prespecified exclusions and assessed fixed-country support and leave-one-country-out influence. No causal effect of the guideline was estimated. Results In 2024, 83,126,427 of 134,806,681 SAC were reported treated (61.7%), compared with 17,368,705 of 118,864,858 adults (14.6%). The SAC indicator combined an 85.2% reporting-denominator share with 72.3% conditional reported coverage; the corresponding adult components were 47.7 and 30.6%. Of the adults represented in the denominator, 34.3% appeared in SAC-only records, potentially reflecting programme scope, and 18.0% in records without an age label. The adult indicator was lower in every year and in every sensitivity analysis. However, programme expectations were not the same throughout the study period: 2014–2021 preceded the broader guideline, whereas 2022–2024 represented the early calendar years following or coinciding with its publication. Logical missing-report envelopes placed the 2024 adult-minus-SAC difference between −61.8 and +5.3 percentage points, leaving the actual ordering of treatment coverage between adults and SAC unidentified. Conclusion The reported adult–SAC difference combines the availability of valid age-specific treatment information with the treatment reported within supported records. A low reporting-denominator share cannot distinguish programme scope from incomplete reporting. Preschool-age treatment was not separately observable. Age-inclusive monitoring requires explicit age categories and documented eligibility and reporting states; these data do not identify verified uptake, individual equity, or causal guideline effects.