An experiment conducted at the Aerosol Research Center of the University of Bristol
Since the pandemic broke out, scientists have been trying to find out exactly how long the virus survives in the air. We have heard hypotheses of all kinds, but an experiment conducted at the Aerosol Research Center of the University of Bristol now seems to determine a turning point: Covid loses 90% of its ability to infect us after 20 minutes, but already after five its strength is halved . In offices, where there is usually a rather dry atmosphere, the virus noticeably decays in just five seconds.
This does not mean that you can finally take off your masks, quite the contrary. The Bristol experiment shows that they are more necessary than ever when we are close to someone. If we enter a bar, the virus will not be transmitted to us by the person sitting at the back of the room, but by the friend with whom we are having coffee, or the barista who serves it to us.
What we thought we knew about the spread of the virus in the air was due to experiments conducted in sealed containers in which Covid molecules had been introduced. Under these conditions, some American scientists had discovered that the virus could be detected even after three hours. But the environment in a sealed tube is not the same as that of the air that circulates outdoors, nor is that of housing structures.
In Bristol they used another method, managing to levitate some Covid molecules between two magnetic rings. It has been found that many factors, such as humidity, temperature and ultraviolet rays, affect the duration of the virus’ survival. Every coronavirus needs humidity, which is why it prefers the humid environments of our body, such as the bronchi and lungs. When the viral particles leave the mouth or nose, they leave their ideal microclimate, humid and rich in carbon dioxide, and dry quickly. Increased levels of oxygen in the air also result in a deleterious rapid rise in their pH.
These two conditions are sufficient to significantly reduce the ability of the virus to infect other people, while keeping it dangerous at close range and in particular environmental conditions. The rate at which the particles dry depends on the humidity of the air: when it is below 50%, as in most offices, the virus loses about half its ability to infect in just five seconds and loses another 19. % in the next five minutes. At 90% humidity, that of a steam sauna, 52% of the particles were still active after five minutes.
“People have been concerned about poorly ventilated spaces and airborne transmission meters or across a room. I don’t want to say it doesn’t happen, but I think the greatest risk of exposure occurs when you are close to someone, Professor Jonathan Reid, lead author of the study, told The Guardian. When you are away from an infected person, not only is the aerosol diluted, but there is also less infectious material because the virus has lost power over time “.
The study hasn’t been peer-reviewed yet, but it confirmed many of the things scientists have discovered in the field: spacing protects against infection, face masks are a must when you’re close to someone, but they don’t make any sense on a street. uncrowded.
The ventilation of the rooms remains important, to avoid any accumulation of infectious particles. “Aerosols quickly fill internal spaces in the absence of adequate ventilation – said Stephen Griffin, professor of virology at the University of Leeds – so assuming that the infected individual remains inside the room, the levels of spread of the virus they will be continuously reintegrated ».
In the Bristol experiment, the main mutations of Covid were tested, but not yet Omicron. The latest variant has more tools to infect people, but stops in the bronchi without ramping up the lungs. But it may also have found a way to survive longer in the air in order to spread more, and it would be important to know.
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