Beware of using invalid transmission models to guide HIV health policy
Authors: Justin T Okano, Sally Blower
Journal: The Lancet Global Health (2014)

Jeffrey Eaton and colleagues (January, p e23)1Eaton JW Menzies NA Stover J et al.Health benefits, costs, and cost-effectiveness of earlier eligibility for adult antiretroviral therapy and expanded treatment coverage: a combined analysis of 12 mathematical models.Lancet Glob Health. 2014; 2: e23-e34Summary Full Text Full Text PDF PubMed Scopus (158) Google Scholar used modelling to inform international guidelines for antiretroviral therapy for HIV. Specifically, they undertook a comparative cost–effectiveness analysis based on predictions from 12 independent transmission models: seven were used for South Africa, four for Zambia, four for India, and one for Vietnam. They concluded that all 12 models show similar results—that earlier eligibility for antiretroviral therapy is cost effective.1Eaton JW Menzies NA Stover J et al.Health benefits, costs, and cost-effectiveness of earlier eligibility for adult antiretroviral therapy and expanded treatment coverage: a combined analysis of 12 mathematical models.Lancet Glob Health. 2014; 2: e23-e34Summary Full Text Full Text PDF PubMed Scopus (158) Google Scholar They implied that their consensus finding increases confidence in the use of modelling results to guide HIV health policy. The comparative consensus modelling approach used by Eaton and colleagues is now used frequently to justify the implementation of particular HIV interventions.1Eaton JW Menzies NA Stover J et al.Health benefits, costs, and cost-effectiveness of earlier eligibility for adult antiretroviral therapy and expanded treatment coverage: a combined analysis of 12 mathematical models.Lancet Glob Health. 2014; 2: e23-e34Summary Full Text Full Text PDF PubMed Scopus (158) Google Scholar, 2Hontelez JA Lurie MN Barnighausen T et al.Elimination of HIV in South Africa through expanded access to antiretroviral therapy: a model comparison study.PLoS Med. 2013; 10: e1001534Crossref PubMed Scopus (94) Google Scholar, 3van de Vijver DA Nichols BE Abbas UL et al.Preexposure prophylaxis will have a limited impact on HIV-1 drug resistance in sub-Saharan Africa: a comparison of mathematical models.AIDS. 2013; 27: 2943-2951Crossref PubMed Scopus (57) Google Scholar However, this approach produces meaningful results only if the comparison is based on valid models. Most comparative consensus studies (including that by Eaton and colleagues) have not checked for model validity. We checked the validity of the seven South African models that Eaton and colleagues used by reproducing some of their numerical simulations (figure). A valid model should accurately reflect the current state of the epidemic. Notably, we show that not all of the South African models agree on the present state of the epidemic; consequently, they cannot all be valid. Two models estimate that, at present, the epidemic (ie, incidence) is fairly stable, three that it is gradually decreasing, and two that it is rapidly decreasing (figure). One can only have confidence in the results from a comparative analysis if it is based on valid models. Only then can a comparative consensus approach be useful to guide health policy. We declare that we have no competing interests. We acknowledge the financial support of the National Institute of Allergy and Infectious Diseases, National Institutes of Health (grant R01 AI041935). Health benefits, costs, and cost-effectiveness of earlier eligibility for adult antiretroviral therapy and expanded treatment coverage: a combined analysis of 12 mathematical modelsOur estimates suggest that earlier eligibility for antiretroviral therapy is very cost effective in low-income and middle-income settings, although these estimates should be revisited when more data become available. Scaling up antiretroviral therapy through earlier eligibility and expanded coverage should be considered alongside other high-priority health interventions competing for health budgets. Full-Text PDF Open AccessBeware of using invalid transmission models to guide HIV health policy – Authors' replyWe agree with Justin Okano and Sally Blower that every effort must be made to ensure that important policy decisions are informed by valid models. Full-Text PDF Open Access