ABSTRACT The uptake of HIV pre-exposure prophylaxis (PrEP), a highly effective prevention intervention, remains low among adolescent girls and young women (AGYW, ≥16-24 years) in Africa, a priority population for HIV prevention interventions. Compared to other populations, African AGYW are at increased risk of HIV infection; in Kenya, AGYW account for 33% of the total of new HIV infections yet comprise only 10% of the population. Barriers to PrEP initiation for AGYW are multi-faceted and include institutional (e.g., stigma associated with use) and intra-personal (e.g., lack of PrEP knowledge or self-efficacy) barriers. Innovative PrEP delivery models that can help overcome these barriers are needed. The opinion of peers often influences the behaviors and preferences of AGYW; the majority of AGYW who have initiated PrEP in Africa to date have done so because of informal peer referral. HIV self-testing (HIVST) is a new technology that has the potential to enhance peer PrEP referral. Much of the emphasis on HIVST to date has been on identifying new individuals living with HIV and facilitating linkage to treatment interventions, but most individuals who self-test will test negative and may be interested in facilitated linkage to prevention interventions. We hypothesize that a formalized peer PrEP referral + HIVST delivery model (developed during the K99 phase of the R00 parent award) can amplify PrEP initiation among Kenyan AGYW at HIV risk. In this supplement application, the research aims of the R00 parent award have remained unchanged. The first aim, which has been completed, pilot tested and refined an intervention where Kenyan AGYW using PrEP (i.e., peer providers) referred their peers (i.e., peer clients) to PrEP following a formalized training on peer referral paired with distribution of HIVST kits. The pilot found that this intervention had high feasibility and acceptability. The second aim, which is ongoing, is measuring the effect of a refined version of this intervention (based on Aim 1 findings) on PrEP initiation among AGYW in a 2-arm hybrid effectiveness-implementation cluster-randomized controlled trial (cRCT). The control arm of this cRCT is informal word-of-month peer PrEP referral and the trial is measuring both effectiveness (e.g., PrEP adherence) and implementation (e.g., adoption, fidelity, cost) outcomes. To date (from May 3 to September 15, 2023), 35 peer providers (44% of the targeted 80) have enrolled in the cRCT. However, unexpected implementation challenges – including approval delays, participant recruitment challenges, national civil unrest, and supply chain challenges – have made cRCT recruitment and enrollment much slower than expected. Thus, we are requesting an administrative supplement to ensure we can reach our final trial endpoints and generate high-quality evidence that indicates whether the proposed intervention increases PrEP initiation among an important population at HIV risk (i.e., AGYW). The findings from th...