- We are learning about the new coronavirus every day.
- One of the current questions concerns its possible seasonality. In this case, it could do less damage during the summer but return in the fall, like other coronaviruses.
- UV lamps are used to clean operating theaters and could be of great help in cleaning large areas. But not for humans, because UV rays are very dangerous.
Will this dangerous Covid-19 melt like snow in the sun this summer? Will he come back to investigate us in the fall, like the other coronaviruses responsible for colds? Many questions still surround the possible fragility of this virus to heat, humidity and UV ... and therefore its seasonality.
But this hypothesis interests many scientists and will be decisive in the future, to know if we will have to live with this coronavirus for many more years until a vaccine is not found.
Sensitive to heat?
"It is possible that this virus (Sars-CoV-2) is partly sensitive to certain climatological aspects which could play a role", said Jean-François Delfraissy, president of the scientific council Covid-19, on the television channel LCP April 15, but "there are still many unknowns".
For Gilles Pialoux, head of the infectious and tropical pathologies service at the Tenon hospital (AP-HP), these untruths must be turned away that make believe that high temperatures and UV rays make it possible to suppress the coronavirus. "First, because it circulates in hot countries, in African countries, in Australia," he argues. Then, it is true that coronaviruses are sensitive to temperatures, but from 60 ° C. There are few countries with such heat! Third argument: another coronavirus, the Seas (Middle East Respiratory Syndrome Coronavirus), appeared in Saudi Arabia, where it is very hot. "In a press release on the fake news surrounding this coronavirus, the World Health Organization specifies that" you can contract COVID-19 in any climate, even in hot or sunny weather. Countries with warm climates have reported cases of COVID-19. "
But it would be too simple if the debate ended there. While it is clear that living in low temperate climates does not prevent meeting the virus, other researchers suggest that the coronavirus is sensitive to high temperatures and UV. Indeed, an American study presented at the end of April assured that it weakens in a hot and humid atmosphere as well as under the rays of the sun. "Our most striking observation to date is the powerful effect that sunlight seems to have on killing the virus, both on surfaces and in the air," said a senior security official. American interior, Bill Bryan. Previous studies had shown that the virus survived better in cold and dry weather conditions rather than hot and humid. "Reasonably, we can say that this virus is less dangerous with summer temperatures, between 20 and 30 ° C", confirms Laurent Lagrost, research director at Inserm.
Does this mean that this coronavirus would be seasonal? Researchers are skipping over this question and we will only be able to answer it a posteriori, in 2021 perhaps ... "We can fear a reduction in the epidemic during the summer in the Northern Hemisphere, with a displacement towards the southern hemisphere, which we already see at the moment, underlines Laurent Lagrost. But it would be a virus reservoir with a possible return in the fall. "
A season is a set of parameters, insist the two researchers: temperature, humidity and ultraviolet. And not only! There is also a societal side. "The question arises as to whether we can have a seasonal improvement, not linked solely to the weather," says Gilles Pialoux. But related to social distancing. When everyone is out in the open, schools are closed, and less public transportation is used, viruses may circulate less than in the fall. "
Sensitive to UV?
"Everything that is pathogenic, bacteria, viruses, is sensitive to ultraviolet rays and in particular to UV-C", assures Laurent Lagrost. Ultraviolet rays, invisible to men, are broken down into three wavelengths. UV-B and UV-C are stopped by the ozone layer, while UV-A is filtered less efficiently by the atmosphere.
In this case, should you dry your laundry, and in particular reusable masks, outside in the sun? "Exposing personal effects to the open air and the sun increases the chances of making the virus unsustainable," says Laurent Lagrost. Especially since Sars-COV-2 has a lipid monolayer on the surface which contributes to its stability, and this structure does not like solvents, hence inactivation with soap. And he probably also doesn't like UV rays, which cause damage to part of the virus and break its infection capacity. For him, therefore, it is a safe bet that these UV represent an asset for humans in order to get rid of it. But beware of amalgams. Because hanging out your clothes and putting your shoes outside has nothing to do with roasting in the sun while thinking of keeping this virus away from yourself ... “Obviously, we don't invite anyone to expose themselves to the sun for hours. UV rays are very dangerous for the skin and cause melanomas. UV radiation will never cure anyone when you are infected. On the other hand, exposing your personal effects to the sun may be a reasonable recommendation. "
Robots that clean surfaces with UV
For this Inserm researcher, this property of ultraviolet rays is also interesting to exploit to clean surfaces. "UV-C is" virucidal ", it is known. Some countries have systematized the use of UV-C lamps to decontaminate public spaces: trains, metro corridors, operating theaters. These robots can move and process a large space, without forgetting corners and systematically. "
The Alsatian company Concept Light is working on prototypes of UV-C lamps to clean meeting rooms, offices, restaurant tables… "UV-C disinfection has been used for thirty years, but with the mercury lamp, explains Victor Vincentz, manager of the company. The novelty is that we are in the process of developing UV-C led lamps. Advantage? A more ecological tool (because the lamp lasts longer), more effective for disinfecting and less dangerous because the LED is not likely to explode, and it diffuses a blue light which lets people know that it is important not to return in the room as long as the robot works, pleads this company. "These lamps emit high energy UV radiation which can cause severe skin burns, but also damage the cornea and the retina of the eye," said the CEO. These disinfections must therefore be done at night, and without human presence…
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