Date Published: May 22, 2019
Publisher: Public Library of Science
Author(s): Deven T. Hamilton, Eli S. Rosenberg, Samuel M. Jenness, Patrick S. Sullivan, Li Yan Wang, Richard L. Dunville, Lisa C. Barrios, Maria Aslam, Steven M. Goodreau, Joan A. Caylà.
Pre-exposure prophylaxis (PrEP) is an effective and safe intervention approved for use to prevent HIV transmission. PrEP scale-up strategies and clinical practice are currently being informed by modeling studies, which have estimated the impact of PrEP in adult and adolescent MSM populations separately. This partitioning may miss important effects or yield biased estimates by excluding dependencies between populations.
We combined two published models of HIV transmission among adults and adolescent MSM. We simulated an HIV epidemic among MSM aged 13–39 without PrEP, with PrEP for adult MSM ages (19–39) and with the addition of PrEP for adolescents ages (16–18), comparing percent of incident infections averted (impact), the number of person-years on PrEP per infection averted (efficiency), and changes in prevalence.
PrEP use among eligible 19–39 year old MSM averted 29.0% of infections and reduced HIV prevalence from 23.2% to 17.0% over ten years in the population as a whole. Despite being ineligible for PrEP in this scenario, prevalence among sexually active 18 year-olds declined from 6.0% to 4.3% due to reduced transmissions across age cohorts. The addition of PrEP for adolescents ages 16–18 had a small impact on the overall epidemic, further reducing overall prevalence from 17.0% to 16.8%; however prevalence among the sexually active 18 year-olds further declined from 4.3% to 3.8%.
PrEP use among adults may significantly reduce HIV prevalence among MSM and may also have significant downstream effects on HIV incidence among adolescents; PrEP targeting adolescents remains an important intervention for HIV prevention.
Preexposure prophylaxis (PrEP) is an effective and safe intervention to prevent human immunodeficiency virus (HIV) [1–4]. The FDA first approved Truvada (Emtricitabine and Tenofovir Disoproxil Fumarate) for HIV PrEP among adults in 2012  and the CDC clinical practice guidelines, issued in 2014, indicate PrEP use for sexually-active adult MSM with substantial HIV acquisition risk . The potential impact of these policies has been demonstrated through modeling, which found that their application within a population of 18–39 year-old MSM could avert a significant number of HIV infections—33% in their baseline scenario . The potential impact of PrEP on new HIV infections has also been demonstrated empirically, e.g. a recent analysis of new diagnoses among all persons ≥ 13 years of age in the US found that PrEP uptake is associated with a reduction in new HIV infections at the state level .
We combined two published stochastic dynamic network models, one for ASMM, defined as ages 13–18 , and one for adult MSM, defined here as ages 19–39 . In short, we modeled an open cohort of ~13,500 13–39-year-olds (500 per 1-year age). We modeled sexual relationship formation and dissolution; sexual behavior within relationships (anal sex acts, condom use, role selection); HIV testing; HIV treatment initiation, adherence and cessation; PrEP initiation, adherence and discontinuation; transmission; intrahost viral dynamics; and demographic change (entry, aging, death and exit). The partnership networks were modeled using separable temporal exponential random graph models [31, 32]. At each time step (one- week) new partnerships could form, old partnerships could dissolve, and individuals engaged in within partnerships sexual decision making and behaviors. The model was implemented using the EpiModel platform (www.epimodel.org) . Additional model details are provided in the supplemental material (S1 Appendix); here we detail elements that differ from those already published elsewhere [7, 18]. All simulation code and analysis scripts are available online at https://github.com/statnet/PrEP-for-ASMM-and-adult-MSM.
In the baseline scenario (no PrEP), the prevalence of HIV in the sexually active population was 23.2% (95% CrI: 21.4%, 24.5%) with incidence of 322.7 (95% CrI: 292.8, 344.2) per 10K person years at risk over 10 years (Table 1). With the inclusion of adult PrEP per CDC guidelines at 40% coverage among eligible adult MSM, there were on average 3,760 (95% CrI 3,660, 3,839) adult MSM on PrEP at any time. Over 10 years, overall prevalence declined to 17.0% (95% CrI: 15.7%, 18.0%), a 26.7% reduction; incidence declined to 206.4 (95% CrI: 187.4, 220.7) per 10K person years at risk; and 693 (95% CrI: 574, 820) infections were averted per 100K person years at risk, a PIA of 29.0% (95% CrI: 24.0%, 34.4%). The NNT was 33 (95% CrI: 27, 40). The average age at HIV acquisition increased only slightly from 25.9 (s.d. = 6.2) to 26.0 (s.d. = 6.6).
This study models the impact of PrEP targeted at both adult MSM and ASMM on the HIV epidemic. We model the sexual life course from debut through the first half of adulthood to focus specifically on impacts of PrEP that may not be captured when adult and adolescent populations are modeled independently.