At a humidity of less than 50 percent – such conditions prevail in offices, for example – the virus lost around half of its infectivity within five seconds. After that, the decline was slower and more even, and was an additional 19 percent for the next five minutes.
At a humidity of 90 percent – which corresponds to a steam bath or a shower – the decline in infectivity was slower: 52 percent of the particles were still infectious after five minutes, after 20 minutes it was only about ten percent. And after that there was no longer any difference between the two conditions.
No data on Omikron
The temperature of the air had no effect on infectivity, which contradicts the popular belief that transmission is lower at high temperatures.
The effects have been seen with several SARS-CoV-2 variants, including alpha. The team hopes to start experiments with the Omikron variant in the coming weeks.
Distance rules and the wearing of masks are therefore the most effective means of preventing infection, according to the authors. Ventilation measures are also useful, but are likely to have a lesser effect.
“People have focused in poorly ventilated rooms and thought about airborne transmission for several meters or across a room. I’m not saying that isn’t happening, but I think that is still the greatest risk of contagion that you are close to someone, “says Reid.
“As you move further away, not only is the aerosol diluted, but there are also fewer infectious viruses because the virus becomes less infectious over time.”