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1. Assessment of epidemic projections using recent HIV survey data in South Africa: A validation analysis of ten mathematical models of HIV epidemiology in the antiretroviral therapy era

Author

Eaton, J.W. (Jeffrey), Bacaër, N. (Nicolas), Bershteyn, A. (Anna), Cambiano, V. (Valentina), Cori, A. (Anne), Dorrington, R.E. (Rob E), Fraser, C. (Christophe), Gopalappa, C. (Chaitra), Hontelez, J.A.C. (Jan), Johnson, L.F. (Leigh), Klein, D.J. (David), Phillips, A. (Andrew), Pretorius, C. (Carel), Stover, J. (John), Rehle, T.M. (Thomas M), Hallett, T.B. (Timothy), Eaton, J.W. (Jeffrey), Bacaër, N. (Nicolas), Bershteyn, A. (Anna), Cambiano, V. (Valentina), Cori, A. (Anne), Dorrington, R.E. (Rob E), Fraser, C. (Christophe), Gopalappa, C. (Chaitra), Hontelez, J.A.C. (Jan), Johnson, L.F. (Leigh), Klein, D.J. (David), Phillips, A. (Andrew), Pretorius, C. (Carel), Stover, J. (John), Rehle, T.M. (Thomas M), and Hallett, T.B. (Timothy)

Abstract

Background: Mathematical models are widely used to simulate the effects of interventions to control HIV and to project future epidemiological trends and resource needs. We aimed to validate past model projections against data from a large household survey done in South Africa in 2012. Methods: We compared ten model projections of HIV prevalence, HIV incidence, and antiretroviral therapy (ART) coverage for South Africa with estimates from national household survey data from 2012. Model projections for 2012 were made before the publication of the 2012 household survey. We compared adult (age 15-49 years) HIV prevalence in 2012, the change in prevalence between 2008 and 2012, and prevalence, incidence, and ART coverage by sex and by age groups between model projections and the 2012 household survey. Findings: All models projected lower prevalence estimates for 2012 than the survey estimate (18·8%), with eight models' central projections being below the survey 95% CI (17·5-20·3). Eight models projected that HIV prevalence would remain unchanged (n=5) or decline (n=3) between 2008 and 2012, whereas prevalence estimates from the household surveys increased from 16·9% in 2008 to 18·8% in 2012 (difference 1·9, 95% CI -0·1 to 3·9). Model projections accurately predicted the 1·6 percentage point prevalence decline (95% CI -0·3 to 3·5) in young adults aged 15-24 years, and the 2·2 percentage point (0·5 to 3·9) increase in those aged 50 years and older. Models accurately represented the number of adults on ART in 2012; six of ten models were within the survey 95% CI of 1·54-2·12 million. However, the differential ART coverage between women and men was not fully captured; all model projections of the sex ratio of women to men on ART were lower than the survey estimate of 2·22 (95% CI 1·73-2·71). Interpretation: Projections for overall declines in HIV epidemics during the ART era might have been optimistic. Future treatment and HIV prevention needs might be greater than previousl

Published
2015
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2. Evaluating the cost-effectiveness of pre-exposure prophylaxis (PrEP) and its impact on HIV-1 transmission in South Africa.

Author

Pretorius C, Stover J, Bollinger L, Bacaër N, and Williams B

Subjects
Adolescent, Adult, Age Factors, Algorithms, Cost-Benefit Analysis statistics & numerical data, Epidemics economics, Female, HIV Infections economics, HIV Infections epidemiology, Humans, Incidence, Male, Middle Aged, Models, Economic, Prevalence, Sex Factors, South Africa epidemiology, Young Adult, Epidemics prevention & control, HIV Infections transmission, HIV-1
Abstract

Background: Mathematical modelers have given little attention to the question of how pre-exposure prophylaxis (PrEP) may impact on a generalized national HIV epidemic and its cost-effectiveness, in the context of control strategies such as condom use promotion and expanding ART programs., Methodology/principal Findings: We use an age- and gender-structured model of the generalized HIV epidemic in South Africa to investigate the potential impact of PrEP in averting new infections. The model utilizes age-structured mortality, fertility, partnership and condom use data to model the spread of HIV and the shift of peak prevalence to older age groups. The model shows that universal PrEP coverage would have to be impractically high to have a significant effect on incidence reduction while ART coverage expands. PrEP targeted to 15-35-year-old women would avert 10%-25% (resp. 13%-28%) of infections in this group and 5%-12% (resp. 7%-16%) of all infections in the period 2014-2025 if baseline incidence is 0.5% per year at 2025 (resp. 0.8% per year at 2025). The cost would be $12,500-$20,000 per infection averted, depending on the level of ART coverage and baseline incidence. An optimistic scenario of 30%-60% PrEP coverage, efficacy of at least 90%, no behavior change among PrEP users and ART coverage less than three times its 2010 levels is required to achieve this result. Targeting PrEP to 25-35-year-old women (at highest risk of infection) improves impact and cost-effectiveness marginally. Relatively low levels of condom substitution (e.g., 30%) do not nullify the efficacy of PrEP, but reduces cost-effectiveness by 35%-40%., Conclusions/significance: PrEP can avert as many as 30% of new infections in targeted age groups of women at highest risk of infection. The cost-effectiveness of PrEP relative to ART decreases rapidly as ART coverage increases beyond three times its coverage in 2010, after which the ART program would provide coverage to more than 65% of HIV(+) individuals. To have a high relative cost-effective impact on reducing infections in generalized epidemics, PrEP must utilize a window of opportunity until ART has been scaled up beyond this level.

Published
2010
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