The virus is best transmitted over short distances, and masks and physical distance are probably the most effective ways to prevent infection.
The coronavirus loses almost 90 percent of its ability to infect us within five minutes of arriving in the surrounding air, the first simulations of the virus’s ability to survive in exhaled air have shown, writes the Guardian.
This study reiterates that the virus is best transmitted over short distances, which means that masks and physical distance are probably the most effective ways to prevent infection. Space ventilation, while still important, is likely to play a minor role.
“People were focusing on poorly ventilated areas and thinking about transmitting the virus by air at a distance of several meters across the room. “I’m not saying it does not happen, but you are still at the highest risk when you are very close to infected people,” said Professor Jonathan Reed, director of the Center for Aerosol Research at the University of Bristol.
“As you move away, not only does the aerosol dilute, but the viruses become less contagious as they lose their infectivity over time,” he said.
So far, our assumptions about how long the virus can survive in small droplets of aerosol have been based on studies in which viruses are injected into a closed container called a “Goldberg drum” that rotates to keep the virus in the air.
Using this method, US researchers have discovered that the infectious virus can be detected in the air even after three hours. But such experiments do not copy what exactly happens when we cough or sneeze.
Instead, researchers at the University of Bristol have developed equipment that allows them to generate large numbers of tiny particles containing viruses that float between two electrical rings for five seconds to 20 minutes, controlling ambient temperature, humidity and UV intensity.
“This is the first time anyone has been able to simulate what happens to an aerosol during the exhalation process,” Reed said.
The study, which has not yet been reviewed, suggests that viral particles leave relatively moist and carbon-rich conditions in the lungs, lose water and dry out very quickly, while the transition to lower CO2 levels is associated with a rapid increase in pH.
Both of these factors impair the virus’s ability to infect human cells. However, it should be noted that the speed at which viral particles dry also depends on the relative humidity of the surrounding air.
When the humidity was less than 50 percent – which is similar to most offices – the virus lost its infectivity within 10 seconds, after which the infectivity decreased more slowly but was more persistent.
At 90 percent humidity – roughly equal to a sauna or shower – the loss of infectivity was gradual, with 52 percent of the particles remaining contagious after five minutes, while after 20 minutes about 10 percent of the particles remained contagious.
However, air temperature did not bring about any change in the infectivity of the particles, contrary to the widely held belief that virus transmission is lower during hot weather.
“It would mean that if I met my friends over a drink tonight, the main risk is that I would pass the virus on to my friends or they to me, not that we would be infected by someone who is also in a cafe or a room across the street.” said Reed.
This emphasizes the importance of wearing masks in cases where people can not maintain physical distance.
Similar effects have been observed in all three variants of Sars-CoV-2 virus tested so far, including alpha. Scientists hope to begin experiments with the omicron variant in the coming weeks.
