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AbstractIntroductionOver one hundred implementation studies of HIV pre‐exposure prophylaxis (PrEP) are completed, underway or planned. We synthesized evidence from these studies to inform mathematical modelling of the prevention cascade for oral and long‐acting PrEP in the setting of western Kenya, one of the world's most heavily HIV‐affected regions.MethodsWe incorporated steps of the PrEP prevention cascade – uptake, adherence, retention and re‐engagement after discontinuation – into EMOD‐HIV, an open‐source transmission model calibrated to the demography and HIV epidemic patterns of western Kenya. Early PrEP implementation research from East Africa was used to parameterize prevention cascades for oral PrEP as currently implemented, delivery innovations for oral PrEP, and future long‐acting PrEP. We compared infections averted by PrEP at the population level for different cascade assumptions and sub‐populations on PrEP. Analyses were conducted over the 2020 to 2040 time horizon, with additional sensitivity analyses for the time horizon of analysis and the time when long‐acting PrEP becomes available.ResultsThe maximum impact of oral PrEP diminished by over 98% across all prevention cascades, with the exception of long‐acting PrEP under optimistic assumptions about uptake and re‐engagement after discontinuation. Long‐acting PrEP had the highest population‐level impact, even after accounting for possible delays in product availability, primarily because its effectiveness does not depend on drug adherence. Retention was the most significant cascade step reducing the potential impact of long‐acting PrEP. These results were robust to assumptions about the sub‐populations receiving PrEP, but were highly influenced by assumptions about re‐initiation of PrEP after discontinuation, about which evidence was sparse.ConclusionsImplementation challenges along the prevention cascade compound to diminish the population‐level impact of oral PrEP. Long‐acting PrEP is expected to be less impacted by user uptake and adherence, but it is instead dependent on product availability in the short term and retention in the long term. To maximize the impact of long‐acting PrEP, ensuring timely product approval and rollout is critical. Research is needed on strategies to improve retention and patterns of PrEP re‐initiation.

BackgroundUpdated World Health Organization guidelines have amplified debate about how resource constraints should impact monitoring strategies for HIV‐infected persons on combination antiretroviral therapy (cART). We estimated the incremental benefit and cost effectiveness of alternative monitoring strategies for east Africans with known HIV infection.MethodsUsing a validated HIV computer simulation based on resource‐limited data (USAID and AMPATH) and circumstances (east Africa), we compared alternative monitoring strategies for HIV‐infected persons newly started on cART. We evaluated clinical, immunologic and virologic monitoring strategies, including combinations and conditional logic (e.g., only perform virologic testing if immunologic testing is positive). We calculated incremental cost‐effectiveness ratios (ICER) in units of cost per quality‐adjusted life year (QALY), using a societal perspective and a lifetime horizon. Costs were measured in 2008 US dollars, and costs and benefits were discounted at 3%. We compared the ICER of monitoring strategies with those of other resource‐constrained decisions, in particular earlier cART initiation (at CD4 counts of 350 cells/mm3rather than 200 cells/mm3).ResultsMonitoring strategies employing routine CD4 testing without virologic testing never maximized health benefits, regardless of budget or societal willingness to pay for additional health benefits. Monitoring strategies employing virologic testing conditional upon particular CD4 results delivered the most benefit at willingness‐to‐pay levels similar to the cost of earlier cART initiation (approximately $2600/QALY). Monitoring strategies employing routine virologic testing alone only maximized health benefits at willingness‐to‐pay levels (> $4400/QALY) that greatly exceeded the ICER of earlier cART initiation.ConclusionsCD4 testing alone never maximized health benefits regardless of resource limitations. Programmes routinely performing virologic testing but deferring cART initiation may increase health benefits by reallocating monitoring resources towards earlier cART initiation.

HIV modelling and economic analyses have had a prominent role in guiding programmatic responses to HIV in sub-Saharan Africa. We reflect critically how the HIV modelling field might develop in future. We argue for HIV modelling to be more routinely aligned with national government and ministry of health priorities, recognizing their legitimate mandates and stewardship responsibilities, for HIV and other wider health programmes. We also place importance on an environment existing in which collaboration between modellers, and joint approaches to addressing modelling questions, becomes the norm rather than exception. Such an environment can accelerate translation of modelling analyses into policy formulation because areas where models agree can be prioritized for action, whereas areas over which uncertainty prevails can be slated for additional study, data collection and analysis. We also argue the need for HIV modelling to increasingly be integrated with the modelling of health needs beyond HIV, particularly in allocative efficiency analyses, where focusing on one disease over another may lead to worse health overall. Such integration may also enhance partnership with national governments whose mandates extend beyond HIV and to all of health care. Finally, we see a need for there to be substantial and equitable investment in capacity strengthening within African countries, so that African researchers will increasingly be leading modelling exercises. Building a critical mass of expertise, strengthened through external collaboration and knowledge exchange, should be the ultimate goal.