PROJECT SUMMARY This longitudinal, mixed methods study investigates the relationship between disaster-related stressors, social determinants of health, and health outcomes among HIV-positive people who use drugs (PWUD) in Ukraine and the strategies that health and social service providers have adopted to maintain access to care. In Ukraine, people who use drugs (PWUD) and live with HIV are a vulnerable population and PWUD are a key population in Ukraine’s HIV epidemic, with at least 38% of all people with a new HIV diagnosis and at least 50% of all people living with HIV (PLWH) indicating injection drug use as the route of transmission. Russia’s unprovoked invasion of Ukraine in February 2022 precipitated massive immediate and potentially long-term disruptions to all aspects of daily life in Ukraine, with unknown consequences for HIV-positive PWUD. Russia’s war on Ukraine is both a disaster and a form of mass trauma that involves widespread destruction, loss of life, and psychological distress for those directly and indirectly affected by it. The impact of mass traumas may have disproportionately negative consequences for already vulnerable populations, including those who are economically precarious and socially marginalized. Social determinants of health—the social conditions and economic circumstances that influence health—are key contributors to HIV care and treatment outcomes. The specific aims of this study are: (1) 1. To measure the effects of disaster-related stressors (personal, interpersonal, and environmental) and mediating effects of SDOH and adaptation on primary clinical outcomes of HIV care engagement, ART adherence, and viral suppression and secondary outcomes of drug treatment engagement and risky substance use in a longitudinal cohort followed up to 3 years; (2) To qualitatively characterize at baseline and longitudinally the effects of conflict on social determinants of health and adaptation trajectories of HIV-positive PWUD; and (3) To explore how service providers who work with PWUD and PLWH modify policies and practices in the context of supply chain disruptions, workforce depletion, and population displacement to promote continued care engagement. This project will use an innovative instrumental variables approach to assess how mass trauma and resulting changes to SDOH causally affect substance use and HIV outcomes and link these findings to structural and resources changes that resulted from the war. This approach will leverage a natural experiment in which residence in areas of Ukraine most affected by the war (proximal to the frontlines) approximates a random assignment to mass trauma exposure. Identifying how people remain connected to HIV and substance use care in contexts of disruption and the strategies that health care and social service providers use to keep people engaged have potential broad transferability. The immediate and longer-term consequences of mass trauma for HIV outcomes are unknown. Identifying how pe...