Exploring Overlapping Factors Behind Never Treatment in Mass Drug Administration for PC-NTDs: A Scoping Review v1

Mass drug administration (MDA) is an important strategy for the control and elimination of five neglected tropical diseases (PC-NTDs) including lymphatic filariasis, onchocerciasis, schistosomiasis, soil-transmitted helminths, and trachoma. While high treatment coverage is essential for the success of MDA, a persistent subset of individuals who report never receiving treatment—referred to as "never treated"—poses a significant barrier to elimination efforts. This scoping review aims to identify and synthesize the range of factors, including overlapping and context-specific determinants, associated with never treatment in MDA programs for PC-NTDs. We will searchMEDLINE, Embase, SCOPUS, Global Health, and CINAHL for English and French-language studies of any year. Eligible studies include primary qualitative and quantitative research that investigate never treatment or related concepts such as systematic noncompliance, zero dose, or systematic non-adherence. Data extraction will follow a standardized form, and findings will be thematically synthesized. Key outcomes include the definitions of never treatment used in the literature and thematic categories of contributing factors. This review will offer a comprehensive overview of what is known about never treatment in MDA, supporting efforts to design more inclusive andeffective NTD elimination strategies.