The ComCor study is a nationwide case-control study which aims first to describe the locations and circumstances of recent SARS-CoV-2 infection, and second, to assess the role of different settings and activities in the acquisition of recent SARS-CoV-2 infection. Case recruitment via email from the National Health Insurance Agency in France began in October 2020 and has recruited over 160000 participants to date. Controls are individuals recruited from the Ipsos market research database matched to cases by age, sex, region, population density and exposure period.
The description of SARS-CoV-2 acquisition focuses on the demographic characteristics of cases, the reasons for testing, their adherence to infection prevention and control measures and isolation, and the circumstances of infection.
In the first descriptive analysis of the first 77,000 recruited cases up to January 2021, half of the participants knew the person who infected them: predominantly someone in the a household (42%), followed by an extended family member (21%), someone in the work setting (15%), friends (11%) or another setting (11%). Private gatherings with extended family and friends, and working in shared offices, were found to be the most common circumstances of transmission. For 37% of cases infected outside the household, the suspected source of infection was reported to be symptomatic at the time of transmission. This increased to 46% when infection occurred in the workplace.
Adherence to isolation was greater when someone had been infected by another person outside the household, but participants often began isolation only after the results of testing had been received, rather than from the onset of symptoms.
In an analysis of more than 10,000 single interactions that led to infection outside the household, infection most frequently occurred in indoor settings with closed windows (80% of cases), followed by indoor settings with open windows (15%), and outdoor settings(5%).
In the case-control study, controls complete the same questionnaire of sociodemographic factors, behaviors and recent activities as cases, to identify factors associated with recent SARS-CoV-2 infection.
In the first analysis of 3426 cases (with symptom onset between 30 September and 23 November 2020) and 1713 controls, we found an increased risk of infection associated with any additional person living in the household (+16%) ; having children attend daycare (+31%), kindergarten (+ 27%), middle school (+30%), or high school (+18%); attending professional (+15%) or private gatherings (57%); having recently frequented bars and restaurants (+95%), or having practiced indoor sports activities (+36%). We found no increase in risk associated with frequenting shops, cultural or religious gatherings, or with transportation, with the exception of informal carpooling (+47%). The risk of infection varied by occupation, but remote working was associated with a decreased risk of infection (-35%).
First report (December 2020) https://www.pasteur.fr/fr/espace-presse/documents-presse/etude-comcor-lieux-contamination-au-sars-cov-2-ou-francais-s-infectent-ils
Intermediate report (March 2021) https://hal-pasteur.archives-ouvertes.fr/pasteur-03155847
Third report (November 2021) https://www.pasteur.fr/fr/espace-presse/documents-presse/etude-comcor-nouveaux-resultats-lieux-contamination-au-sars-cov-2-analyse-efficacite-vaccins-arn
- Impact of SARS-CoV-2 Delta variant on incubation, transmission settings and vaccine effectiveness: Results from a nationwide case-control study in France. Lancet Reg Health Eur. 2021 Nov;26:100278. doi: 10.1016/j.lanepe.2021.100278.
- Impact of original, B.1.1.7, and B.1.351/P.1 SARS-CoV-2 lineages on vaccine effectiveness of two doses of COVID-19 mRNA vaccines: Results from a nationwide case-control study in France. Lancet Reg Health Eur. 2021 Sep;8:100171. doi: 10.1016/j.lanepe.2021.100171.
- Exposures associated with SARS-CoV-2 infection in France: A nationwide online case-control study. Lancet Reg Health Eur. 2021 Aug;7:100148. doi: 10.1016/j.lanepe.2021.100148.
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