Coronavirus loses 90 percent of its ability to infect within 20 minutes of becoming airborne with the majority of the loss occurring within the first five minutes, a new study that simulated how viruses survive in exhaled air has shown.
The findings by Bristol’s Aerosol Research Centre (University of Bristol) re-emphasise the importance of short-range Covid transmission, with physical distancing and mask-wearing likely to be the most effective means of preventing infection.
The researcher noted that the more the virus is exposed to air, the less contagious it gets. The study further noted that the ventilation, though still worthwhile, is likely to have a lesser impact.
“People have been focused on poorly ventilated spaces and thinking about airborne transmission over meters or across a room. I’m not saying that doesn’t happen, but I still think the greatest risk of exposure is when you’re close to someone,” said Prof Jonathan Reid, director of the University of Bristol’s Aerosol Research Centre and the study’s lead author, quoted by The Guardian.
The study, which has not yet been peer-reviewed, is the first of its type to replicate how coronavirus moves in the air after being exhaled.
The researchers created equipment to generate virus-containing particles and enabled them to float between two electric rings for anything between five seconds and 20 minutes in a closely regulated environment to replicate what happens to the virus when it gets airborne.
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According to the research, as virus particles leave the lungs, they shed a lot of water, and the reduced levels of carbon dioxide in the air cause a rapid rise in pH. According to the research paper, it has an impact on the virus’s ability to infect human cells.
“This is the first time anyone has been able to actually simulate what happens to the aerosol during the exhalation process,” Reid said.
The study also revealed that in a typical office setting, where the surrounding humidity is typically less than 50 percent, the virus became half as infectious in under five seconds, after which the loss of infectivity got slower and more constant, with a further 19 percent loss over the next five minutes.
In contrast, the drop is substantially slower in a more humid environment, such as a steam room or shower. The researchers discovered, however, the temperature of the air, on the other hand, had no effect on viral infectivity, contrary to popular opinion that viral transmission is reduced at high temperatures.
“It means that if I’m meeting friends for lunch in a pub today, the primary risk is likely to be me transmitting it to my friends, or my friends transmitting it to me, rather than it being transmitted from someone on the other side of the room,” said Reid. This highlights the importance of wearing a mask in situations where people cannot physically distance, he added.
The same effects were seen across all three Sars-CoV-2 variants the team has tested so far, including Alpha. They hope to start experiments with the Omicron variant in the coming weeks.
