Even at two metres distance, it takes less than five minutes for an unvaccinated person standing in the breath of a person with Covid-19 to become infected with almost 100 per cent certainty. But, if both are wearing well-fitting medical masks, the risk drops dramatically, finds a study.
In a comprehensive study, a team from the Max Planck Institute for Dynamics and Self-Organisation in Gottingen showed that if both the infected and the non-infected person wear well-fitting masks, the maximum risk of infection after 20 minutes is hardly more than one per thousand, even at the shortest distance.
If their masks fit poorly, the probability of infection increases to about four per cent. If both wear well-fitting medical masks, the virus is likely to be transmitted within 20 minutes with a maximum probability of ten per cent.
The study also confirms the intuitive assumption that for effective protection against infection, in particular. the infected person should wear a mask that filters as well as possible and fits tightly to the face.
“We would not have thought that at a distance of several metres it would take so little time for the infectious dose to be absorbed from the breath of a virus carrier,” said Eberhard Bodenschatz, Director at the Max Planck.
At this distance, the breathing air has already spread in a cone shape in the air; the infectious particles are correspondingly diluted. In addition, the particularly large and thus virus-rich particles fall to the ground after only a short distance through the air.
“In our study we found that the risk of infection without wearing masks is enormously high after only a few minutes, even at a distance of three metres, if the infected persons have the high viral load of the Delta variant of the SARS-CoV-2 virus,” Bodenschatz said.
And such encounters are unavoidable in schools, restaurants, clubs or even outdoors.
The team also considered that droplets that people spread when they breathe or speak dry while in the air become lighter. This means that they remain in the air longer but also have an increased virus concentration as equal size droplets directly after release. When inhaled, the opposite happens: the particles take up water again, grow like a drop in the cloud and therefore deposit more easily in the respiratory tract.