Socio-economic inequalities and the COVID-19 epidemic in France: territorial analyses by epidemic wave and by metropolitan area

Background: Previous studies highlighted the relationships between socioeconomic inequalities and the population's risk to become disease or die during COVID-19 epidemic. In France, socioeconomic inequalities vary across metropolitan areas, but little is known if that could explain the spatial disparities observed in terms of incidence and testing rates. We assessed the impact of socioeconomic inequalities on testing and incidence rates of COVID-19 for each metropolitan area and wave. Methods: For each of the 22 metropolitan areas, we relied on socioeconomic variables from census data to define socioeconomic profiles using classification on the principal components. We analysed associations between socioeconomic profiles, testing and incidence rates by epidemic wave from July-2020 to March-2023, using spatialised generalised additive mixed models. We performed meta-regressions to study the distribution of testing and incidence rate ratios (socially deprived vs privileged) across metropolitan areas, according to vaccination rates. Results: Socially deprived metropolitan areas had lower testing rates than privileged, but during wave 4 (July-October-2021, extended health pass), testing rates increased in more deprived areas. Incidence rates were higher in deprived areas (waves 2-4, July-2020 to October-2021) but reversed between waves 6 to 9 (March-2022 to March-2023). Meta-regression analysis indicated that high vaccination coverage narrowed testing and incidence gaps between deprived and privileged. Conclusions: The impact of social inequalities on the population's testing and incidence COVID-19 epidemic was driven by socioeconomic inequalities across metropolitan areas and varied across epidemic waves. Vaccination rates and the presence of health measures (lockdowns, health pass) seem to help reduce these disparities. Key words: COVID-19; socioeconomic inequalities; France; geo-epidemiology; testing; incidence; metropolitan area; social deprivation