Project Summary COVID-19 has disproportionately impacted medically or socially vulnerable populations in marginalized urban communities across the United States (e.g., people with co-morbidities, working in high risk settings, those refusing or unable to adhere to the State of New Jersey (NJ) prevention guidelines). Social determinants of health (SDH) such as stigma, incarceration, and poverty are associated with increased exposure to COVID-19 and increased deaths. In the absence of effective, potent, and widely available vaccines and treatments, prevention – i.e., testing, social distancing, contact tracing, and quarantine -- is essential. Little is known about acceptability of COVID-19 testing in low-income and racial/ethnic minority neighborhoods, where residents experience increased barriers to prevention (e.g., inadequate housing, high-risk jobs). However, we have knowledge of cost-effective, evidence-based, and culturally appropriate interventions that have been successfully used to engage people in HIV prevention and treatment. These interventions can be adapted and tested to help address COVID-19. Navigation services (NS) increase HIV testing and adherence to treatment while addressing structural barriers that deter treatment engagement in high-risk communities. Brief counseling increases HIV treatment engagement. This study uses a Sequential, Multiple Assignment Randomized Trial (SMART) with 582 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 public health recommendations. The study aims include: Aim 1: To optimize an adaptive intervention that will increase rates of testing and adherence to NJ COVID-19 recommendations (testing, social distancing, quarantine, hospitalization, contact tracing and acceptance of COVID-19 vaccination) among high-risk populations. Aim 2: To identify predictors of testing completion and adherence to NJ recommendations. This study is innovative in its application of existing evidence-based interventions to address COVID-19 and the use of SMART following Community Based Participatory Research principles. It has