A conceptual framework to model social determinants of COVID-19 vaccination uptake among underserved homeless populations

•People experiencing homelessness have a higher risk of COVID-19 infection, which is linked to several determinants such as unhealthy housing, poor medical cover, and overall insufficient use of healthcare system.•Individuals living in emergency social shelters and those living on the street were less likely to be vaccinated (70.4% and 41.5%, respectively) than participants in migrant worker hostels and those in in accommodation centers (85.9% and 80%, respectively).•Having a personal general practitioner, healthcare cover favorable attitudes towards vaccination (and housing stability are associated with greater vaccine uptake.•actors in the field of underserved homeless population need to implement on-site community-based education campaigns which focus on increasing knowledge about the benefits and efficacy of vaccination. Homeless people have a higher risk of COVID-19 infection, linked to several social, economic and environmental determinants, frequent comorbidities, obstacles to exercising their constitutional social and health rights, poor medical cover, and insufficient use of the healthcare system. Data on COVID-19 vaccine uptake and its main determinants are lacking for this underserved population. To construct and testa conceptual framework to model structural social determinants of COVID-19 vaccine uptake among underserved homeless populations, and to test this model to identify the determinants of COVID-19 vaccine uptake on the homeless population living in two metropolitan areas in France. We implemented a multicenter cross-sectional survey from 15/11/2021 to 22/12/2021 in homeless adults in the city of Marseille and in the greater Paris area.Persons sheltered in migrant worker hostels or in emergency social shelters, members of the COVID HOMELESS cohort study in Marseille, and Travelers living in traditional housing were all eligible. A standardized face-to-face questionnaire was administered to the participants where they lived in various languages by trained interviewers. We used structural equation modeling to analyze the structural social determinants of COVID-19 vaccine uptake, the latter defined as receiving at least one dose. The participation rate was 64 %, accounting for 3811 participants. There were three main factors associated with greater vaccine uptake: i) opportunity, which included having a personal general practitioner (β = 0.05, p