How does the proportion of never treatment influence the success of mass drug administration programmes for the elimination of lymphatic filariasis?

Background Mass drug administration (MDA) is the cornerstone for the elimination of lymphatic filariasis (LF). The proportion of the population that is never treated (NT) is a crucial determinant of whether this goal is achieved within reasonable timeframes. Methods Using two individual-based stochastic LF transmission models, we assess the maximum permissible level of NT for which the 1% mf prevalence threshold can be achieved (with 90% probability) within 10 years under different scenarios of annual MDA coverage, drug combination and transmission setting. Results For Anopheles -transmission settings, we find that treating 80% of the eligible population annually with ivermectin+albendazole (IA) can achieve the 1% mf prevalence threshold within 10 years of annual treatment when baseline mf prevalence is 10%, as long as NT <10%. Higher proportions of NT are acceptable when more efficacious treatment regimens are used. For Culex -transmission settings with a low (5%) baseline mf prevalence and Diethylcarbamazine+Albendazole (DA) or Ivermectin+Diethylcarbamazine+Albendazole (IDA) treatment, elimination can be reached if treatment coverage among eligibles is 80% or higher. For 10% baseline mf prevalence, the target can be achieved when the annual coverage is 80% and NT ≤15%. Higher infection prevalence or levels of NT would make achieving the target more difficult. Conclusions The proportion of people never treated in MDA programmes for LF can strongly influence the achievement of elimination and the impact of NT is greater in high transmission areas. This study provides a starting point for further development of criteria for the evaluation of NT. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The authors are grateful for funding by the Bill & Melinda Gates Foundation through the NTD Modelling Consortium (grant INV-030046). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present work are contained in the manuscript * DA : diethylcarbamazine + albendazole EPHP : elimination as a public health problem GPELF : Global Programme to Eliminate Lymphatic Filariasis IA : ivermectin + albendazole IDA : ivermectin + diethylcarbamazine + albendazole LF : lymphatic Filariasis mf : microfilaria NTD : neglected tropical disease TAS : transmission assessment survey WHO : World Health Organization