According to a new study, the ability of the Coronavirus to infect people begins to decline within five minutes of being airborne, and the virus loses approximately 90% of its infectivity within 20 minutes.
The study, which has yet to be peer-reviewed, is the first to investigate how the virus survives in exhaled air and emphasises the importance of maintaining physical distance and mask-wearing, according to the Guardian.
Ventilation, while still important, is likely to have a smaller impact.
“People have been focused on poorly ventilated spaces and thinking about airborne transmission over metres or across a room. I’m not saying that doesn’t happen, but I think still the greatest risk of exposure is when you’re close to someone,” Prof Jonathan Reid, director of the University of Bristol’s Aerosol Research Centre and the study’s lead author, was quoted as saying.
“When you move further away, not only is the aerosol diluted down, there’s also less infectious virus because the virus has lost infectivity (as a result of time),” he added.
According to the report, researchers from the University of Bristol created an apparatus that allowed them to generate any number of tiny, virus-containing particles and gently levitate them between two electric rings for anywhere from five seconds to 20 minutes, while tightly controlling the temperature, humidity, and UV light intensity of their surroundings.
They discovered that when viral particles leave the relatively moist and carbon dioxide-rich conditions of the lungs, they begin to rapidly lose water and dry out.
The transition to lower CO2 levels is associated with a rapid increase in pH, both of which interfere with the virus’s ability to infect human cells. The speed at which the particles dry out, however, varies depending on the relative humidity of the surrounding air, according to the report.
When this was less than 50% – similar to the relatively dry air found in many offices – the virus lost around half of its infectivity within five seconds, followed by a slower and more steady decline, with a further 19% loss over the next five minutes.
At 90% humidity – roughly equivalent to a steam or shower room – the decline in infectivity was more gradual, with 52% of particles remaining infectious after five minutes, dropping to about 10% after 20 minutes, and there was no difference between the two conditions after that.
However, the study found that air temperature had no effect on viral infectivity, contradicting the widely held belief that viral transmission is reduced at high temperatures, according to the report.
“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 emphasises the significance of wearing a mask in situations where people cannot physically distance themselves, he adds.
The researchers discovered the same effects in all three SARS-CoV-2 variants tested thus far, including Alpha. According to the report, they hope to begin experiments with the Omicron variant in the coming weeks.