Covid loses 90% of ability to infect within five minutes in air – study | Coronavirus

The coronavirus loses 90% of its ability to infect us within five minutes of being airborne, and the world’s first simulations indicate how the virus survives in exhaled air.

The findings reaffirm the importance of short-term transmission of the Covid virus, as physical distancing and mask-wearing are likely to be the most effective means of preventing infection. Although ventilation is still worthwhile, it will likely have less impact.

“People focus on poorly ventilated spaces and think about air moving across meters or across the room. I’m not saying this hasn’t happened, but I think the greatest risk of exposure is when you are,” said Professor Jonathan Reed, Director of the University of Bristol Aerosol Research Center and lead author of the study. close to someone.

“When you move away, not only are the aerosols diluted, but there is a virus that is less contagious because the virus has lost its infectivity. [as a result of time]. “

So far, our assumptions about how long the virus survives in tiny airborne droplets have been based on studies that have involved spraying the virus into airtight vessels called Goldberg barrels, which rotate to keep the droplets airborne. Using this method, US researchers found that the infectious virus could still be detected after three hours. However, such experiences do not accurately replicate what happens when we cough or breathe.

Instead, researchers from the University of Bristol developed a device that allowed them to generate any number of tiny virus-containing particles and gently lift them between two electric loops for anywhere from five seconds to 20 minutes, while tightly controlling temperature, humidity and UV radiation. The intensity of the light from their surroundings. “This is the first time anyone has been able to simulate what happens to an aerosol during exhalation,” Reed said.


The study, which has not yet been peer-reviewed, suggested that because viral particles leave relatively moist and carbon dioxide-rich conditions in the lungs, they quickly lose water and dry up, while moving to lower carbon dioxide levels is associated with a rapid increase in pH These two factors disrupt the virus’s ability to infect human cells, but the speed with which the particles dry varies with the relative humidity of the surrounding air.

When this was less than 50% – similar to the relatively dry air found in many offices – the virus lost half the infection within 10 seconds, after which the decline was slower and more steady. At 90% humidity–roughly equivalent to a steam room or shower–the decrease in infection was more gradual, with 52% of particles still infectious after five minutes, dropping to about 10% after 20 minutes.

However, air temperature did not affect viral infection, contradicting the popular belief that transmission of the virus is lower during warm weather.

“That means if I meet my friends for lunch at a bar today, it will be elementary [risk] I’m more likely to send it to my friends or friends who send it to me, rather than from someone on the other side of the room,” Reed said. This highlights the importance of wearing a mask in situations where people cannot physically distance, he added.

Dr Julian Tang, a clinical virologist at the University of Leicester, said the findings support what epidemiologists have been monitoring on the ground, adding that “Masks are very effective… in addition to social distancing. Improved ventilation will also help – especially if it is close to the source.”

Dr Stephen Griffin, Associate Professor of Virology at the University of Leeds, emphasized the importance of ventilation, saying: “Aerosols will quickly fill indoor spaces in the absence of proper ventilation, so assuming an infected person remains inside the room, levels of virus will be replenished.”

The same effects were seen in all three variants of Sars-CoV-2 the team has tested so far, including Alpha. They hope to begin trials with the Omicron variant in the coming weeks.

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