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Covid-19: can we really predict the evolution of the virus according to temperature and humidity?

2020-12-19T17:58:43.181Z


According to a French study, there is a correlation between low temperature, humid weather and the spread of Covid-19. Many a


Low temperatures (between -3 and 12 degrees) as well as a high humidity rate (60 to 90%) would naturally increase the transmission capacity of the coronavirus.

This is the premise, already mentioned in several studies, on which the company Predict Services, a subsidiary of Météo France specializing in risk management, has been working for nine months.

During her research, put forward by the Minister of Health Olivier Véran last week, she developed an index, the IPTCC (Index Predict of Climatic Transmissivity of Covid-19), fed by "all data from Météo France stations from January to today, ”explains its chairman Alix Roumagnac.

The researchers thus developed an algorithm giving distinct values ​​for temperatures and humidity levels, which they then compared with the number of hospitalizations and deaths due to Covid-19 in France by region.

And the conclusions are more than convincing, according to the leader of Predict Services: "It has been observed on several occasions that very aggravating climatic conditions in terms of Covid-19, correlate with the health situation in certain regions", assures he at the Parisian.

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Covid-19: is there a link between lower temperatures and increased contamination?


He notably cites the example of the Grand-Est and Île-de-France regions, which were very affected during the first wave and in which the IPTCC was "the highest", unlike the French overseas departments and territories and New Aquitaine. , less affected in the spring and which indeed presented "a much less important index".

Another example: in October, during the emergence of the second wave, “the regions with a low index over the whole month, such as Corsica, New Aquitaine, Pays de la Loire and Brittany present indicators less alarming hospital ”.

What explanation can be given to these results?

According to him, hydrometry has an influence on the size of the droplets that carry the virus, “and there is an intermediate range between -3 and 12 degrees, and between 60% and 90% humidity, where the hydrometric conditions allow a persistence of the suspension of droplets in the atmosphere ”.

If the content of this research was validated by further investigations, Alix Roumagnac would like "in the short or medium term, to integrate this parameter in the management of the management of the pandemic", in order "to adapt the recommendations according to the regions" .

"This study can shed light, but it cannot explain everything"

This meteorological index would only be a small part of the explanation, however, in the transmission of Covid-19.

“We quickly learned that the role of climate could exist but that it was not preponderant.

Otherwise, we would not have had the start of an epidemic in March and in May the virus would have almost disappeared, which is not the case in France, ”recalls Pascal Crépey, professor-researcher in epidemiology at the School of advanced studies in public health in Rennes.

However, the specialist considers this study by Predict Services, "interesting, even if it is not definitive", because "it allows to quantify a little more precisely the climatic factor, to strengthen hypotheses".

With reservations: "It would be an error from an epidemiological and public health point of view to think that there is only one factor that explains everything and that in addition it is a climatic factor ...".

"The climate is not necessarily the first factor", also specifies Alix Roumagnac.

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For Mircea T. Sofonea, lecturer in epidemiology and evolution of infectious diseases at the University of Montpellier, this IPTCC should also be taken with some precautions.

“This study can shed light, but it cannot explain everything,” he observes.

There are still a whole bunch of clues that do not take into account, public health policies and especially the weight of human behavior, which, even during the bad season, escapes meteorological data… ”

The specialist, who recalls that seasonality is "well known in respiratory viruses and influenza in particular", confirms that when it is cold and we breathe out air, the droplets likely to contain the virus are " thinner and therefore more prone to suspension in the air ”.

They can then "infect people from a greater distance."

As for the humidity factor, the teacher said he was more reserved: "We lack a strong consensus within the studies carried out".

Indoor folds, dry mucous membranes and vitamin D

Thus, beyond the weather, three major elements must be taken into account to explain an increase in transmissions in autumn and winter, according to him.

In the first place, during these seasons "we have a shorter duration of the day, which inevitably induces a greater presence in the interiors, with less ventilation and therefore an increased risk of infection".

Then, when it's cold, our mucous membranes are drier, underlines the epidemiologist.

They are supposed to be "the first barriers against infections, but when they are dry, they play less of this role and we can be in the presence of viral particles".

In particular those of the coronavirus, if one is near an infected person.

Vitamin D would also be taken into account.

"We know that it plays a role in immunity," insists Mircea T. Sofonea.

However, part of this vitamin is synthesized by exposure to UV rays.

When people are indoors, they are less exposed to the sun.

"

If this study therefore allows to add new light on the climatic factor, it risks, according to epidemiologist Pascal Crépey, not being able to offer much more.

“While this data can most certainly explain why it is easier to control the epidemic in spring than in winter, from an epidemic management point of view, it will not be a game-changer, because the climate is not a factor on which we can have an impact, he admits.

The important thing is to know whether or not we control the epidemic and we have improved a lot since March in terms of management and surveillance.

"

Source: leparis

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