Introduction - Several studies highlight the more severe health and socioeconomic impacts of the COVID-19 pandemic on disadvantaged populations. This could be explained by a combination of factors that may hinder the implementation of SARS-CoV-2 infection prevention measures and adherence to the healthcare pathway. The objective of the ECHO study is therefore to assess knowledge, attitudes, and practices related to the COVID-19 pandemic (preventive measures, vaccination, symptoms, and appropriate actions to take in the event of symptoms), as well as its impact among people in precarious situations living in shelters in France. Method - ECHO is a cross-sectional study conducted in 18 shelters located primarily in the Paris and Lyon regions, from May 2 to June 7, 2020, during the first lockdown and the beginning of the reopening. The questionnaire, in simplified French or English, was administered by interviewers, with the assistance of a telephone interpreter if necessary. Results - A total of 535 participants were included. Good knowledge of COVID-19 symptoms and satisfactory adherence to prevention and management measures for the infection (testing, isolation) were observed in the study population. Factors associated with adopting the recommended behaviors to combat the epidemic were: age, educational level, occupational status, health literacy, length of stay at the center, and region of origin. A significant proportion of patients forgoing care for reasons unrelated to COVID-19, as well as a deterioration in mental health and socioeconomic status, were also observed.