Sunday, June 26

Covid loses 90% of the ability to infect in five minutes in the air: study | Coronavirus


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

The findings re-emphasize the importance of short-range Covid transmission, and physical distancing and wearing masks are likely the most effective means of preventing infection. Ventilation, while still worth it, is likely to have less of an impact.

“People have focused on poorly ventilated spaces and thinking about airborne transmission over meters or through a room. I’m not saying that doesn’t happen, but I think the biggest risk of exposure is when you’re around someone, ”said Professor Jonathan Reid, director of the University of Bristol. Aerosol Research Center and the lead author of the study.

“When you walk away, not only is the aerosol diluted, there is also less infectious virus because the virus has lost infectivity. [as a result of time]. “

So far, our assumptions about how long the virus in tiny droplets survive in the air have been based on studies that involved spraying viruses into sealed containers called Goldberg drums, which spin to keep the droplets in the air. Using this method, the American researchers found that infectious virus could still be detected After three hours. However, such experiments do not accurately replicate what happens when we cough or breathe.

Instead, researchers at the University of Bristol developed a device that allowed them to generate any number of tiny virus-containing particles and gently levitate them between two electrical rings for between five seconds and 20 minutes, while strictly controlling temperature, humidity, and temperatures. UV rays. light intensity of its surroundings. “This is the first time that someone has been able to really simulate what happens to the aerosol during the exhalation process,” Reid said.

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The study, which has not yet been peer-reviewed, suggested that as viral particles leave the relatively humid, carbon dioxide-rich conditions of the lungs, they lose water rapidly and dry out, while transitioning to lower levels of dioxide. of carbon is associated with a rapid increase in pH. Both factors disrupt the virus’s ability to infect human cells, but the rate at which the particles dry varies depending on 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 had lost half its infectivity within 10 seconds, after which the decline was slower and more consistent. At 90% humidity, roughly equivalent to a steam bath or shower, the decrease in infectivity was more gradual, with 52% of the particles remaining infectious after five minutes, dropping to around 10% after 20 minutes.

However, air temperature made no difference in viral infectivity, contradicting the widely held belief that viral transmission is lower during hot weather.

“It means that if I meet friends for lunch in a pub today, the main [risk] it’s likely that I will pass it on to my friends, or my friends will pass it on to me, rather than someone on the other side of the room, ”Reid said. This highlights the importance of wearing a mask in situations where people cannot physically distance themselves, he added.

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

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www.theguardian.com

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