The virus responsible for Covid-19 is evolving. And we evolve with it. Consequently, our knowledge of the epidemic of spring 2020 in France, or even of last winter, is not quite the same as today. This is the subject of the new study by the Institut Pasteur, published in the journal The Lancet Regional Health Europe: understand how and in which situations people got infected, in the era of the Delta variant and mass vaccination.
This work is part of the the ComCor survey, carried out in partnership with the Ipsos Institute and the National Health Insurance Fund and published in April, after two interim reports unveiled in December 2020 and in March 2021. Only the size of the sample and the dates change. The observations took place between May 23 and August 13, partly this summer, after the third wave but during the fourth, with 12,634 infected adults and 5,560 uninfected adults.
Its results, always presented at the same age and sex for the contaminated and the two samples (contaminated and uncontaminated), are not, however, very surprising. Poorly ventilated enclosed spaces, such as bars (+ 90%), nightclubs (reopened at the start of summer), but more generally private parties, contribute to the proliferation of SARS-CoV-2, especially among the less 40 years old (+ 340%). The study mentions in particular the Euro football, among these events promoting indoor gatherings to watch the matches.
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Note a small difference, however, for people over 40 years old. “Children attending daycare, kindergarten, elementary school or middle school were all associated with an increased risk of infection,” the study authors note, with up to 90% increased risk. for a child under 3 years old. Finally, transport (metro, train, taxi and plane) is also associated, for the first time, with an increased risk of contracting the disease, from + 20% for the metro to 70% for the plane (due to the risk of contamination at destination).
On the other hand, this last study reassures on the potential dangerousness of the places of culture or the businesses (except of proximities), closed or with restricted access during previous phases of the epidemic. No over-risk was detected in these places, although mistrust remains in place, these observations dating from this summer when attendance had not necessarily returned to their highest level.
The role of ventilation
“The practical consequence is to remind people of the importance of ventilation and of wearing a mask,” the head of the study, epidemiologist Arnaud Fontanet, told AFP. “Even in places where the sanitary pass is requested, wearing a mask, when possible, remains useful. It would not be absurd to keep it before and after a meal in the restaurant, and it is recommended to wear it to the theater. or in the cinema. In these places, it adds additional protection, he already insisted to L’Express, a week ago. We must put together all the tools at our disposal, especially as all the analyzes show today “The importance of aerosol transmission. Masks and ventilation are therefore essential.” On Thursday, the Minister of Health Olivier Véran announced that wearing a mask will again be compulsory everywhere indoors, even in places subject to the health pass.
But according to the member of the Scientific Council, and particularly for this winter, aeration must also become a “reflex”. “For my part, I open windows everywhere I go. When I am teaching, I open a door and a window to the outside and everyone has a mask. An open door, even on a hallway, makes a difference, “he testified.
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Remarks which do not surprise them either. The issue of ventilation was already at the heart of the debates last winter. It should still be this season. In terms of discoveries, the new study by the Institut Pasteur nevertheless provides a better understanding of the Delta variant and the effectiveness of vaccination, or cure, on the production of antibodies. We have found strong protection against symptomatic Delta for those who have had a previous infection, whether recent (two to six months) or associated with one or two doses of the messenger RNA vaccine. For those who had no previous infection, the protection was lower with two doses of the mRNA vaccine, “note the authors.” Finally, we found that the average incubation period was shorter for Delta than for non-Delta infections (4.3 and 5.0 days, respectively). ”