Project Summary COVID-19 has impacted the health and social fabric of individuals and families living across the United States; and it has disproportionately affected people living in urban communities with co-morbidities, those working in high- risk settings, refusing or unable to adhere to CDC guidelines, and more. Social determinants of health (SDH), such as stigma, racial discrimination, xenophobia, incarceration, and poverty have been associated with increased exposure to COVID-19 and increased deaths. Marginalized communities, defined as low-income and racial/ethnic minority neighborhoods, where residents experience increased barriers (e.g., inadequate housing, high-risk jobs) to prevention and treatment, bear disproportionately higher rates of co-morbidities associated with more severe cases of COVID-19. While effective and potent vaccines are becoming more available, it will take time to reach herd immunity and it is unclear how long newly-developed vaccines provide protection and how effective they are against emerging variants. Therefore, prevention methods recommended by the Centers for Disease Control (CDC) – i.e., testing, hand-washing, social distancing, contact tracing, vaccination, and quarantine -- are essential to reduce the rates of COVID-19 in marginalized communities. Research about COVID-19 testing and vaccine uptake in these communities must occur in real time and it must account for the fast-changing landscape of the pandemic, including the impact of vaccine availability on testing uptake. Two cost-effective, evidence-based, and culturally appropriate interventions have been effective in engaging people in HIV prevention and treatment – these can be adapted and tested to help address COVID-19 prevention needs. Specifically, Navigation Services (NS) have shown to increase HIV testing and adherence to treatment while addressing structural barriers that deter treatment engagement in high-risk communities; and Brief Counseling (BC) has shown to increase HIV treatment engagement. This study uses a Sequential, Multiple Assignment Randomized Trial (SMART) with 1,218 COVID- 19 medically/socially vulnerable people. Guided by the COVID-19 Continuum of Prevention, Care, and Treatment, analysis will explore factors associated with testing and adherence to CDC COVID-19 prevention and treatment recommendations. The study aims include: To examine the effectiveness of an adaptive intervention to increase COVID-19 testing and adherence to CDC-recommendations of preventive behaviors – social distancing, hand- washing, inoculation, mask-wearing, vaccination- on comparable but distinct samples. We will control for baseline, time, demographics and COVID risk; (2) To examine the immediate and medium-term impact of the adaptive intervention on COVID testing and adherence to recommendations by collecting follow-up data at 2,5,12 and 24 weeks post baseline. Implementation aim: To collect intervention implementation data (context, cost, barriers, l...