Estimating the epidemic consequences of HIV prevention gaps among key populations

Abstract

Introduction HIV epidemic appraisals are used to characterize heterogeneity and inequities in the context of the HIV pandemic and the response. However, classic measures used in appraisals have been shown to underestimate disproportionate risks of onward transmission, particularly among key populations. In response, a growing number of modelling studies have quantified the consequences of unmet prevention and treatment needs (prevention gaps) among key populations as a transmission population attributable fraction over time (tPAFt). To aid its interpretation and use by programme implementers and policy makers, we outline and discuss a conceptual framework for understanding and estimating the tPAFt via transmission modelling as a measure of onward transmission risk from HIV prevention gaps; and discuss properties of the tPAFt. Discussion The distribution of onward transmission risks may be defined by who is at disproportionate risk of onward transmission, and under which conditions. The latter reflects prevention gaps, including secondary prevention via treatment: the epidemic consequences of which may be quantified by the tPAFt. Steps to estimating the tPAFt include parameterizing the acquisition and onward transmission risks experienced by the subgroup of interest, defining the most relevant counterfactual scenario, and articulating the time‐horizon of analyses and population among whom to estimate the relative difference in cumulative transmissions; such steps could reflect programme‐relevant questions about onward transmission risks. Key properties of the tPAFt include larger onward transmission risks over longer time‐horizons; seemingly mutually exclusive tPAFt measures summing to greater than 100%; an opportunity to quantify the magnitude of disproportionate onward transmission risks with a per‐capita tPAFt; and that estimates are conditional on what has been achieved so far in reducing prevention gaps and maintaining those conditions moving forward as the status quo. Conclusions The next generation of HIV epidemic appraisals has the potential to support a more specific HIV response by characterizing heterogeneity in disproportionate risks of onward transmission which are defined and conditioned on the past, current and future prevention gaps across subsets of the population.

Country ownership and sustainable programming of the HIV response in South Africa: A scoping review

“…The SANAC commissions external evaluators to conduct the NSP Mid-Term Review and End-Term Review. 15 , 31 The reviews take a highly consultative and participatory approach in which several stakeholders contribute, with a central multisectoral steering committee providing oversight and guidance. Before finalisation and publishing of reports, validation meetings/workshops are held where stakeholders give direct feedback on the findings of the report as well as provide information that might be lacking to be included in the reviews.…”

“…Not addressing the unmet HIV prevention and treatments needs of KPs has negative epidemic consequences. 10 , 31 For example, it is estimated that nearly 50% of HIV infections between 2020 and 2029 would stem from the unmet HIV prevention and treatment needs of FSWs and their clients. 31 …”

Comparison of Empirically Derived and Model-Based Estimates of Key Population HIV Incidence and the Distribution of New Infections by Population Group in Sub-Saharan Africa

“…Substantial research has demonstrated that this cross-sectional representation of HIV acquisition poorly quantifies the epidemiological impacts of effective prevention among key populations by not reflecting network effects and the potential to avoid onward transmission. 15,19,47,48 Counterfactual-based metrics such as the transmission preventable attributable fraction or intervention scenario analysis, whose counterfactual scenario accounts for projected cumulative incidence in all population groups over a longer time horizon, better reflect the benefits of HIV prevention efforts among key populations. 17,[39][40][41] Our finding that mathematical models indicated a lower proportion of infections among key populations than assumed by UNAIDS does not undermine modeling evidence for prioritized interventions among these populations; the same models reporting results in this analysis have consistently found large epidemiologic impact and cost-effectiveness for interventions averting transmission among key populations.…”

Adequate funding of comprehensive community‐based programs for key populations needed now more than ever to reach and sustain HIV targets

“…The contribution of key populations in generalized HIV epidemics has historically been underestimated, largely due to failing to consider differing transmission dynamics [ 8 ]. Evidence suggests that unmet prevention and treatment needs among key populations contribute the highest population‐level long‐term risk of onward transmission [ 9 , 10 ]. Thus, allocating more resources towards filling the “prevention gaps” among key populations could produce the most cost‐effective programming [ 11 , 12 ].…”