A cold wave is currently affecting the north of France, with snowfall in places.
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Olivier MORIN / AFP
A cold wave is currently affecting the entire northern part of France.
Traditional virus outbreaks, such as influenza or bronchiolitis, usually develop in winter.
Under these conditions, one can wonder if the negative temperatures will not increase the circulation of the virus?
"20 Minutes" takes stock.
Down to -6 ° C in Hauts-de-France and Grand-Est, -5 ° C in Ile-de-France, -2 ° C in Normandy… A cold wave sets in on the northern half of France for a few days, Météo France alerted on Wednesday, which placed twenty-three departments in snow and ice orange vigilance and four in extreme cold orange vigilance.
If the circulation of the virus slowed, this summer, it resumed with more vigor in the fall, leading to a second containment at the end of October.
For some specialists, the epidemic resumption is linked to the drop in temperatures.
Faced with the cold wave that affects part of France, should we fear an increase in contamination?
20 Minutes
takes stock.
Has a link between lower temperatures and increased circulation of the virus been established?
Yes.
In a preliminary study, published on January 26, 2021, the Institut Pasteur notes "a significant dependence of the transmission of SARS-CoV-2 on the weather" and on the climate.
According to the laboratory, the R0, the famous reproduction rate of the virus, increases by 0.16 for each degree lost under an average temperature of 10 ° C.
"The second wave in the countries of the north-western hemisphere was probably triggered by the transition from summer to winter conditions," said the Institut Pasteur in its preliminary study.
Will the cold snap increase contamination?
Not necessarily.
If the virus likes the cold, it obviously does not like the extreme cold.
According to a study published at the end of 2020 by Predict Services, a Montpellier subsidiary of Météo France and Airbus, the virus would spread less when temperatures are very low.
"When it is very cold, less than three degrees, the droplets tend to fall to the ground", or to freeze, and therefore to be less disseminated, explained the Minister of Health, Olivier Véran, in mid-December on France 5 This is also valid when it rains or when it snows, the droplets falling faster to the ground.
❄ Can a cold snap relaunch the epidemic?
The minister @OlivierVeran evokes the Montpellier scientific study of Predict ⬇️ # Cà You pic.twitter.com/KXW7rtezyP
- C to you (@ cavousf5) December 17, 2020
However, the cold is not the only one having an impact.
According to the Predict Services study, the humidity level also plays a big role in the spread of Covid-19.
"When the air is very humid, the droplets that carry the virus tend to rise and spread, when the air is very dry, the droplets that carry the virus fall to the ground", also detailed Olivier Véran, on the plateau of "C to You".
Is there an ideal temperature for the transmission of the virus?
Yes.
It is the combination of low temperatures (but not too much) and humidity that would favor the transmission of the virus.
“Between 3 ° C and 12 ° C and 60 to 90% humidity, the droplets on which the virus attaches will tend to remain suspended in the air.
It can contribute to stronger transmission, ”explains Alix Roumagnac, president of Predict, a subsidiary of Météo France and Airbus.
His company relied on an article by two researchers from the Massachusetts Institute of Technology (MIT) from March 2020 to develop an index of "climate transmissivity of Covid-19".
This index explains the “heterogeneous development of the pandemic” according to the regions of the world and the seasons, according to Alix Roumagnac.
In recent weeks, the index has also been sent regularly to the Directorate General of Health (DGS) for analysis.
Data which would also explain why Brittany is relatively spared.
In this region, it is "the oceanic mildness and the rain" which would thus prevent the droplets carrying the virus from remaining suspended in the air, according to Alix Roumagnac.
Does human behavior in the face of the cold affect transmission?
Again, yes.
The colder it is, the more the population stays inside, explained the epidemiologist, Pascal Crépey, to our colleagues from BFMTV: "When it is cold we ventilate less, we stay more indoors, in closed places. where the air is not renewed.
Another factor: our immune defenses.
In winter, our organisms are less resistant and more likely to catch infections.
Conversely, in summer, the air is rather dry, our bodies are a little more resistant and our activities are done more outdoors.
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