Antiretroviral treatment, prevention of transmission, and modeling the HIV epidemic: why the ART efficacy and effectiveness parameter matters

Introduction HIV remains a major public health threat with over 75 million deaths, 2 million annual infections and over 1 million HIV-associated TB cases a year. Population-based studies suggest a marked decline in incidence, prevalence and deaths, mostly likely due to treatment expansion, in countries in East and Southern Africa. This calls into question the ART efficacy, effectiveness and coverage parameters used by many modelers to project HIV incidence and prevalence. Methods For 2015 and 2016 we reviewed global and national mathematical modeling studies regarding ART impact (with or without other HIV prevention interventions) and/or 90-90-90 on either new HIV infections or investment or both. We reviewed these HIV epidemiologic and costing models for their structure and parameterization around ART; we directly compared two models to illustrate differences in outcome. Results The nine models published in 2015 or 2016 included parameters for ART effectiveness ranging from 20% to 86% for ART effectiveness. Model 1 limits eligibility for ART initiation to 80% coverage of people living with HIV and with a CD4+ cell count below 350 cells/μL, 70% retention, and ART reduces transmission by 80%, with a derived ART effectiveness of 20%. Model 2 assumes 90-90-90 by 2020 (i.e., 73% viral suppression of estimated PLHIV), ART reduces transmission by 96% in those on ART and virally suppressed, and by 88% in those on ART but not virally suppressed with a derived effectiveness of 86% and consequent decline towards ending AIDS and HIV elimination. ART parameter selection and assumptions dominate and low ART effectiveness translates into lower impact. Discussion Using more realistic parameters for ART effectiveness suggests that through expanding access and supporting sustainable viral suppression it will be possible to significantly reduce transmission and eliminate HIV in many settings.