Abstract Social inequalities in health affect access to healthcare and prevention. In Marseille, these inequalities are pronounced, with 26% of the population below the poverty line. In September 2022, a health mediation and outreach program was launched in deprived neighbourhoods to promote cancer screening and vaccination by going towards populations and providing information and orientation adapted to individuals’ health literacy and autonomy. We aimed to evaluate the effectiveness of this intervention. A repeated cross-sectional study compared knowledge, attitudes and practices about cancer screening and vaccination before and after health mediation interventions and between control and intervention neighbourhoods. Trained investigators administered a questionnaire door-to-door to individuals aged 18-74 years in randomly selected households. A first T0 survey was conducted in September 2022, and a second T1 survey is underway in May 2024, in 13 intervention and 26 control neighbourhoods. We compared the before-and-after participation rates and associated risk factors for cancer screening and vaccination between both areas using mixed regression models. Of the 2,647 respondents at T0, 61% were women, 43% non-native French speakers, 40% unemployed, and 53% had public health insurance. Survey respondents were socially deprived and had lower participation rates in cancer screening and vaccination compared to national levels. At T0, the cancer screening participation rate was 31% for colorectal cancer, 51% for breast cancer, and 68% for cervical cancer. Factors associated with non-participation were not believing in the effectiveness of cancer screening, not being aware of its existence or not speaking French. At T0, only 54% knew about human papillomavirus vaccine and only 35% of eligible women were vaccinated. A comparison of these T0 results with results of the ongoing T1 survey will be presented, in order to assess the effectiveness of this health mediation intervention. Key messages • Health mediation promotes cancer screening and vaccination by going towards populations in deprived neighbourhoods and providing information adapted to individuals’ health literacy and autonomy. • Survey respondents were socially deprived and had lower participation rates in cancer screening and vaccination compared to national levels.