A national mixed-mode seroprevalence random population-based cohort on SARS-CoV-2 epidemic in France: the socio-epidemiological EpiCov study

Abstract

Background: the EpiCov study, initiated at the end of the first national lockdown in France, aimed to provide national and regional estimates of the seroprevalence of SARS-CoV-2 infection, and to analyze relations between living conditions and the dynamics of the epidemic. We present and discuss here the survey methodology, and describe the first-round fieldwork. Method: 371,000 individuals aged 15 years or more were randomly selected from the national tax register, stratified by departments, including three overseas departments, and by poverty level with over-representation of people living below the poverty line. Health, socio-economics, migration history, and living conditions were collected through self-computed-assisted web interviews or via computer-assisted telephone interviews. The first-round survey was conducted in May. A random subsample was eligible to receive material for home blood self-sample on dried blood spot (DBS), in order to detect IgG antibodies against the spike protein (Euroimmun ELISA-S), and neutralizing antibodies for non-negative ELISA-S. For the second-round conducted in November, all respondents were eligible for the antibodies detection from home DBS sample, as well as the other household members aged 6 years or more for 20% of them. Participation and adjustment for nonresponse: 134,391 respondents completed the first-round questionnaire from May 2 to June 1, 2020, including 16,970 (12.6%) respondents under the poverty line. Multimodal web/tel interviews was randomly assigned to 20% of the sample. The other were assigned to exclusive CAWI. Overall 17,441 respondents were eligible for home blood sample, among them 12,114 returned the DBS (interquartile date: May 25- June 5). The response probability was first estimated from logit models adjusted on a wide range of auxiliary demographic and socio-economic variables available from the sampling frame, and final weights calibrated to the margins of the population census permitted to correct for a large part of the non-response bias. Conclusion: The Epicov study is one of the largest national random population-based seroprevalence cohort, with both an epidemiological and sociological approaches to evaluate the spread of the COVID-19 epidemic, and the impact on health and living conditions. One of the major interests of this study is the broad coverage of the socio-economic and territorial diversity of the population.

The social specificities of hostility toward vaccination against Covid-19 in France

“…The results published in the study have been adjusted by applying the weights established by the National Institute of Statistics and Economic Studies (INSEE) and marginal recalibration in the survey and sampling design to correct for non-participation, so as to produce estimators that are representative of the population. More information about the cohort can be found in another publication [ 10 ].…”

Social inequalities and dynamics of the early COVID-19 epidemic: a prospective cohort study in France

“…All analyses were weighted using a Heckman model to take into account the effect of the response mode on the reporting of COVID-19-like symptoms. 21 Analyses were performed with the SAS software V.9.4. A p value <0.05 was considered statistically significant.…”

Trends in social exposure to SARS-Cov-2 in France. Evidence from the national socio-epidemiological cohort – EPICOV

“…Final calibrated weights were calculated to correct for non-response, as detailed elsewhere (Warszawski et al, 2021), for first and second round. Response homogeneity groups were derived from the sampling weight divided by the probability of response estimated with logit models adjusted for auxiliary variables potentially linked to both the response mechanism and the main variables of interest in the EpiCov survey.…”