From May 23 to August 13, 2021, the Institut Pasteur, in partnership with the French National Health Insurance Fund (CNAM), Santé publique France and the Ipsos institute, conducted the fourth part of the ComCor epidemiological study on circumstances and places of infection with the SARS-CoV-2 virus in France. The aim of the study was to identify the socio-demographic factors, places visited and behaviors associated with a higher risk of infection with SARS-CoV-2. The study was also used to carry out a real-world analysis of the effect of previous infection with COVID-19 and the efficacy of messenger RNA vaccines against symptomatic infection with the Delta variant. The findings were published in The Lancet Regional Health Europe on November 26, 2021.
In the fourth part of the ComCor study, the data of 12,634 individuals who tested positive for SARS-CoV-2 between May 23 and August 13, 2021 and 5,560 non-infected controls recruited over the same period and matched by age, sex, population density, region of residence and week of exposure were analyzed. The recruited individuals completed a self-administered questionnaire. The period under study coincided with the gradual reopening of public places and the emergence of the Delta variant in mainland France. The results describe the circumstances of infection for diagnosed cases of SARS-CoV-2. Of the 12,634 people who tested positive, 8,644 (68%) were diagnosed as having been infected with the Delta variant.
The study also enabled real-life estimations to be made, for France, about the protective effect of previous infection with COVID-19 and the effectiveness of vaccines against symptomatic SARS-CoV-2 infection caused by the Delta variant.
The period under study, from May 23 to August 13, was characterized by the following events:
May 19th: Reopening of museums, cultural places and outdoor facilities (bars & restaurants, sports centers)
June 9th: Reopening of nightclubs ("Health pass" required)
August 9th: "Health pass" extended to all public settings
Circumstances and places of SARS-CoV-2 transmission
The analysis identified indoor bars and private parties as places of transmission of the Delta variant in people aged under 40 between June 9 and July 9, with a higher risk for men than for women. This period coincided with the Euro 2020 football championship, suggesting that supporters gathering together for matches may have played a role in spreading the virus, as was also observed in the United Kingdom. When nightclubs opened, they were also places of transmission.
In people aged over 40, those with children in their household or close circle were at greater risk of infection, with the risk ranging from +30% for middle school children to +90% for very young children (under the age of three).
Certain modes of transport were also associated with a moderate increase in the risk of infection: sharing a car with family and friends (+30%) (excluding car-sharing platforms, for which no increased risk of infection was observed), taxis (+50%), metro (+20%), train (+30%) and flying (+70%).
No additional risk of infection was recorded for cultural venues, shops (excluding local shops), restaurants (it was a period during which many restaurants mainly used outdoor seating areas or well ventilated indoor areas), places of worship, sports activities and family gatherings (excluding weddings, for which an increased risk was recorded).
These results emphasize the importance of compliance with hygiene and distancing measures, especially wearing masks and airing closed premises.
Real-world analysis of the protective effect of previous infection with COVID-19 and the effectiveness of vaccines against symptomatic infection with the Delta variant
The study revealed that protection conferred by previous infection is 95% if the infection occurred within the past 6 months; this rate falls to 74% if the infection occurred more than 6 months ago.
As documented in other international studies, two doses of mRNA vaccine confer less protection against symptomatic forms of the Delta variant, with efficacy waning over tim...
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