Over 10 million American households have fallen behind on rent or are ≥3 months behind on mortgage payments during COVID-19. These households are disproportionately low-income and twice as likely to be home to racial or ethnic minorities compared to whites. The City of St. Louis, MO is using its American Rescue Plan (HR1319) allocation to establish a rent-relief helpline and support fund to assist such households. We will build upon this unique opportunity with an innovative cross-sector project to ask rent-relief helpline callers about COVID-19 vaccination and testing, and evaluate strategies to help them with both. In Aim 1 we will determine the COVID-19 vaccination rate of housing-unstable adults in St. Louis. In Aim 2, we will evaluate the impact of targeted messages on unvaccinated callers’ getting vaccinated. In Aim 3, we will evaluate a proven sequential request strategy to elicit in-home COVID-19 testing among those who are not interested in getting vaccinated. The study was jointly conceived with existing RADxUP and CEAL community partners, draws upon the RADxUP Coordinating Center and consortium of grantees to access testing technology, uses common data elements, and is highly responsive to priorities outlined in the FOSI. Because many communities across the U.S. will be establishing similar rent-relief programs and services, findings from the proposed study have the potential for wide application, integrating vaccination and testing into social services.