The sun, heat and coronavirus: the White House announces a study encouraging

Soleil, chaleur et coronavirus: la Maison Blanche annonce une étude encourageante

The new coronavirus can be degraded in a few minutes in the Sun, according to an experiment done by a laboratory of high security u.s. government and touted by Donald Trump, but the scientific community questioned the methodology and the interest of this result.

The presentation was made Thursday at the White House by the scientific advisor to the department of homeland Security, Bill Bryan, during a press conference with the american president.

According to the single table presented, Sars-Cov-2, the scientific name for the coronavirus causing the disease COVID-19, loses half of its particles in less than two minutes when it is under a summer Sun, in the air or on surfaces, according to a simulation made in a box replicating the rays of the sun.

“That’s the impact of UV rays on the virus,” said Bill Bryan.

The laboratory which carried out the experience, the National Biodefense Analysis and Countermeasures Center, specializing in the threats of bioterrorism, is a laboratory of biosafety level maximum (4).

Its researchers have also tested the resistance of the virus to various conditions of temperature and humidity inside.

Indoors, under normal conditions (21-24°C, 20% humidity), the “half-life” of the virus on surfaces such as door handles is 18 hours (one hour in the air). This is reduced to one hour, pushing the heat to 35°C and humidity at 80%.

The main question on this presentation is related to the fact that the study has not been published. Normally, the scientists write an article describing their method and their results and submit them for assessment to a reading committee.


“It would be good to know how the test was done “, told AFP Benjamin Neuman, a biologist at the university of Texas A&M-Texarkana. “Not because it would necessarily be bad, but because there are different methods for counting viruses “.

In general, virologists have established that the Sun’s ultraviolet rays (A and B) could inactivate viruses, because they can damage the genetic material of cells and viruses (DNA or RNA): it is for this reason that we put on sunscreen.

“The study confirms what we know about the other virus envelope “, told AFP Vincent Racaniello, a professor of virology at Columbia university.

“It is known that the UV radiation and the high temperatures kill the viral particles on the surfaces, and the particles of coronaviruses are no exception to the rule,” said England Penny Ward, a member of the british faculty of pharmaceutical medicine.

But this does not mean that any dose of UV kills any virus, in any condition.

In 2004, the researchers exposed the Sars coronavirus, a cousin caused an outbreak in 2003, to UVA for 15 minutes, and it was not inactivated.

There is another tranche of UV, UVC, whose effectiveness is proven since a long time to kill the microbes, but these UVC are produced by special lamps, because the UVC from the Sun are completely filtered by the atmosphere.

These lamps are used to disinfect medical equipment, but may not be used on the skin, because the UVC is extremely harmful.

Regarding the heat and humidity, the new study would reinforce the few others who have assessed their effect on Sars-Cov-2.

Experiments in the laboratory indicate a reduction in the survival of Sars-Cov-2 at elevated temperatures “, wrote a group of experts consulted by the u.s. Academies of sciences in a letter to the White House on 7 April. But they have warned that such experiments could not ever reproduce the real world.

Researchers note finally that the interest of the disinfection by the Sun is limited, the contamination of the outside being considered less likely to occur indoors and in confined spaces.

The big question regarding the possible seasonality of the coronaviruses.

Officials from the White House hope that their data on the heat signal a braking of the virus this summer.

Several studies have separately found a correlation between the speed of propagation of the COVID-19 and the climatic conditions, the latitude or UV exposure of the country, with an epidemic is slower in warmer climates and moist…

But the Academies of science u.s. encourage ” prudence “, because of the lack of objectivity and the quality of the data.

They also note that of the ten influenza pandemics in the past 250 years, ” the two have started the winter in the northern hemisphere, three in the spring, two in summer and three in the fall “.

“All of them have a peak of the second wave about six months after the emergence of the virus in the human population, irrespective of the date of introduction “.

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