Study increases understanding of airborne transmission

The infectivity rate of the novel coronavirus greatly reduces within seconds of exposure to the air, and falls by 90 percent within 20 minutes of becoming airborne, scientists in the United Kingdom have found.

The research, which was published on the preprint server MedRxiv and is yet to be peer reviewed, challenges previous thinking about how long the virus can survive while airborne, and its ability to infect people in shared spaces.

Researchers from Bristol University say that the virus loses infectivity by 50 to 60 percent within seconds of being released into the air.

Previous studies involving less-sophisticated methods had posited that active virus could hang around in the air for hours.

The new study indicates that people are much more likely to catch the virus from someone they are near to, rather than by inhaling viral particles circulating in the air from a more distant source.

"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," Jonathan Reid, a professor at Bristol and lead author on the study, told The Guardian newspaper, which first reported the research.

The study suggests social distancing and mask-wearing are two of the best ways to prevent spread, and that ventilation may not play a major role in preventing spread across long distances.

"People have been focused on poorly ventilated spaces and thinking about airborne transmission over meters or across a room," Reid said. "I'm not saying that doesn't happen, but I think still the greatest risk of exposure is when you're close to someone."

Christopher Lee, an infectious disease expert and Malaysia health department advisor who was not involved in the research, said on Twitter the new study "re-emphasizes the importance of short-range spread" and that social distancing and masks are "likely the most effective prevention".

The Bristol team developed a special machine to help with the research, which allowed them to accurately assess the interaction of viral particles with the air.

Previous research into the airborne spread of COVID-19 primarily involved an apparatus called a Goldberg drum, which tests how long a virus can survive in an enclosed space. These tests revealed novel coronavirus could remain active in the air for hours.

But the apparatus developed by the Bristol team introduces a precise number of viral particles into a sealed chamber where they levitate in an electric field. It allows for adjustments to humidity, light, and heat, which allows researchers to more accurately model viral survivability in real-world environments.

Through this method, the scientists were able to ascertain that the novel coronavirus is far more susceptible to drying out and losing infectivity than previously thought, with infectivity more accurately measured in seconds and minutes, rather than hours.