PROJECT SUMMARY/ABSTRACT Background: In sub-Saharan Africa (SSA), adolescent girls and young women (AGYW) 15-24 years of age remain at epicenter of the HIV epidemic, with more than 270,000 new HIV infections each year. Biomedical HIV prevention strategies like tenofovir-based oral pre-exposure prophylaxis (PrEP) are promising measures for reducing HIV acquisition in AGYW. However, providing PrEP to all 100 million AGYW in SSA is not feasible, economical, or necessary, as the risk of HIV acquisition among AGYW is not uniformly high. Risk assessment tools are needed to identify those AGYW sub-populations at greatest risk for acquiring HIV in order to support targeted PrEP program implementation. Existing risk assessment tools for HIV incidence in AGYW have had important limitations surrounding feasibility, validity, and generalizability. The primary goal of this project is to develop a regional risk assessment tool for AGYW that is feasible to implement, valid, and generalizable. Our overarching premise is that risk of HIV acquisition among AGYW is not uniform and it is possible to identify high risk AGYW at a regional level. Aims and Methods: Using nationally representative data from 13 African countries collected as part of the Population-based HIV Impact Assessment (PHIA) initiative, our team will address this premise through three specific aims. In the first aim, we will explore risk factors associated with recent HIV infection, a marker of incident HIV, among AGYW. Recent infection is defined in the PHIA data using a well-established testing algorithm. Using data from 13 PHIA surveys from 2015-2019, which include >50,000 observations, individual, structural, household, and epidemiologic predictors of recent HIV infection among AGYW will be identified. In the second aim, we will use the candidate predictors from the first aim to develop and internally validate a risk assessment tool to identify AGYW at highest risk of HIV acquisition. In the third aim, we will externally validate the risk assessment tool in five second-round PHIA surveys from 2020. Team: The team, led by an early-career Principal Investigator, has expertise in HIV prevention for AGYW, biomedical HIV prevention, risk score development, and advanced methods for complex survey data. The team is supported by a technical advisory panel of experts from multiple SSA regions. Expected Impact: These findings will provide an in-depth understanding of the current transmission dynamics of HIV among AGYW in SSA. At the end of the study, we expect to have a validated clinical risk assessment tool that can be applied to a range of SSA settings. Such a tool has the potential to transform the clinical delivery of PrEP and other biomedical HIV prevention strategies in SSA.