Covid-19 could in theory evolve, like other viruses with respiratory transmission, on a seasonal basis in temperate countries. Thus, summer is generally a period of calm on this front. No flu or colds between June and September.
SARS-CoV-2 is an exception to this rule. However, “laboratory studies have shown that this virus does not like high temperatures or humidity and that its infectivity decreases when it is exposed to UV,” recalls Professor Vincent Maréchal.
Work that analyzes transmission levels as a function of climatic conditions would confirm that, “viral circulation is strongest when the virus is in an environment between 0 ° C and 17 ° C. “
The gloomy weather of this summer does it alone explain the maintenance of a significant circulation of the virus?
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Various parameters
In reality “many other parameters come into play”, underlines Prof. Maréchal. Among them, we can cite “the variation in the sensitivity of the mucous membranes to infections during cold and dry periods, pollution which can worsen the clinical course, the behavior of individuals, the contagiousness of variants and the immunity of populations …” He is therefore “difficult to associate the dynamics of the epidemic with the weather,” he said.
Admittedly, the summer is generally gloomy but “the virus was already circulating last summer”, he recalls. And this when the weather had been much warmer and sunny.
This year, “the presence of the Delta variant which has a level of contagiousness much higher than historical forms” also plays a role in maintaining the pandemic.
This variant is 40 to 60% more contagious than the British variant, itself much more contagious than the historical form.
Moreover, even if the weather is not always good, people’s behavior changes during this holiday period.
Family reunions, reunions with friends, outings promote transmission, whatever the weather. And barrier gestures now fall much more often, even between unvaccinated people.
With in addition, a significant tourist flow which helps to circulate the virus between the territories.
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Vaccination and barrier measures
There remains the question of the impact of vaccination. As of August 8, more than 37 million people have been immunized with a complete regimen in the country.
However, they can also be infected and transmit the virus, even if the risk of transmission is considered to be much lower than for those who are not. It is therefore important to remain cautious and to maintain barrier gestures in all circumstances.
An opinion shared by the World Meteorological Organization which considers that “it is advisable not to rely on the meteorological and climatic conditions, in particular the beginning of the increase in temperatures in the northern hemisphere in the spring, to relax the measures aimed at to curb the spread of the virus ”.
Thus, according to this analysis *, “it is the measures taken by the public authorities (such as the compulsory wearing of a mask and travel restrictions) rather than the meteorological factors that would have regulated the dynamics of the transmission of Covid-19 in 2020 and early 2021 ”.
* Analysis of the influence of meteorological and air quality factors on Covid-19
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