BACKGROUND: Migrants, people experiencing homelessness (PEH), or precariously housed (PH) are at high risk for COVID-19 infection, hospitalization, and death from COVID-19. However, while data on COVID-19 vaccine uptake in these populations are available in the USA, Canada, and Denmark, we are lacking, to the best of our knowledge, data from France. METHODS: In late 2021, we carried out a cross-sectional survey to determine COVID-19 vaccine coverage in PEH/PH residing in Ile-de-France and Marseille, France, and to explore its drivers. Participants aged over 18 years were interviewed face-to-face where they slept the previous night, in their preferred language, and then stratified for analysis into three housing groups (Streets, Accommodated, and Precariously Housed). Standardized vaccination rates were computed and compared to the French population. Multilevel univariate and multivariable logistic regression models were built. RESULTS: We find that 76.2% (95% confidence interval [CI] 74.3-78.1) of the 3690 participants received at least one COVID-19 vaccine dose while 91.1% of the French population did so. Vaccine uptake varies by stratum, with the highest uptake (85.6%; reference) in PH, followed by Accommodated (75.4%; adjusted odds-ratio = 0.79; 95% CI 0.51-1.09 vs. PH) and lowest in Streets (42.0%; AOR = 0.38; 95%CI 0.25-0.57 vs. PH). Use for vaccine certificate, age, socioeconomic factors, and vaccine hesitancy is associated with vaccination coverage. CONCLUSIONS: In France, PEH/PH, and especially the most excluded, are less likely than the general population to receive COVID-19 vaccines. While vaccine mandate has proved an effective strategy, targeted outreach, on-site vaccinations, and sensitization activities are strategies enhancing vaccine uptake that can easily be replicated in future campaigns and other settings. Vulnerable populations, such as people experiencing homelessness, are less likely to have a COVID-19 vaccine. We aimed to identify potential reasons for this, by interviewing homeless/precariously housed people in France. We found that although most homeless people have been vaccinated, vaccination rates are lower than the general population. Among the homeless, the least likely to be vaccinated are those living on the streets. The need for vaccine certificates and the support of social workers are positive drivers of vaccine uptake, while influence from family/friends, vaccine hesitancy and fear of the vaccine negatively affect uptake. Providing vaccines on-site and tailoring programs to better target these vulnerable groups should be priorities. Raising awareness by involving trusted third parties is also key to countering negative vaccine beliefs. Our insights apply beyond the COVID-19 crisis, when routinely supporting the health of vulnerable populations. engRead less <