PROJECT SUMMARY White Mountain Apache-Navajo-JHU research partners are uniquely positioned and prepared to advance COVID-19 prevention science through the Emergency Competitive Revisions for Community-Engaged Research on COVID-19 Testing among Underserved and/or Vulnerable Populations (NOT-OD-20-121). Since April 2020, we have implemented comprehensive COVID-19 mitigation activities with Navajo and White Mountain Apache nations, who have had the highest rates in the US, and honed capacity for home-testing and obtaining rapid results. Our experience and data review with tribal divisions of health and the Indian Health Service has uncovered barriers to testing, protective behaviors, isolation and care-seeking among two high risk sub-groups that must be addressed for successful mitigation. The first group are elders, ages >65, who have the highest case fatality rate in both communities and are deeply revered as teachers of cultural practices and languages. A significant portion of elders are currently resistant to testing due to cultural beliefs and fear, and slow to seek care when symptoms worsen. The second group are young adults, ages 18-34, using substances, who have the highest proportion of cases per capita, are less likely to social- distance or isolate, and are more transient, moving among multi-generational households. This project will apply a 2x2 factorial design to evaluate two interventions for these high-risk groups: 1) a culturally tailored, age-specific Motivational Interviewing (MI) intervention to promote testing, protective behaviors and appropriate isolation and care-seeking, and 2) a COVID-19 symptom (CS) text-based monitoring system designed to shorten time between symptom onset and testing, while incorporating GIS to assist with route-mapping for home-based follow-up. MI has strong evidence in American Indian communities, including our team’s proven MI intervention for improved STI/HIV testing. The CS System builds on our experience with mobile health surveillance and embedded GIS/GPS tracking. Our three primary aims are: 1: Use Community Based Participatory Research to apply knowledge of relevant facilitators and barriers to create, pilot, implement, and evaluate through an RCT a culturally tailored brief MI intervention to promote COVID-19 testing when experiencing symptoms, appropriate preventive behaviors, and isolation and care-seeking when positive among elders (ages >65 years) and young adults with a recent history of substance misuse; 2: Implement and evaluate through a RCT a daily CS monitoring system with alerts, mechanisms for participants to request home-testing when experiencing first symptoms, and GIS routing for those responding to text-based alerts; and 3: Evaluate the relative merits of MI or CS alone or combined on testing and time to testing when experiencing symptoms, and adherence to isolation and care-seeking recommendations when positive using a 2x2 factorial design. Our secondary aims will explore if a)...