Here; an excerpt:
If both the infected and the non-infected person wear well-fitting FFP2 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 percent. If both wear well-fitting medical masks, the virus is likely to be transmitted within 20 minutes with a maximum probability of ten percent. 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.
The infection probabilities determined by the Max Planck team indicate the upper limit of the risk in each case. "In daily life, the actual probability of infection is certainly 10 to 100 times smaller," says Eberhard Bodenschatz. This is because the air that flows out of the mask at the edges is diluted, so you don't get all the unfiltered breathing air. But we assumed this because we can't measure for all situations how much breathing air from one mask wearer reaches another person, and because we wanted to calculate the risk as conservatively as possible," Bodenschatz explains. "Under these conditions, if even the largest theoretical risk is small, then you're on the very safe side under real conditions." For the comparative value without the protection of a mask, however, the safety buffer turns out to be much smaller. "For such a situation, we can determine the viral dose inhaled by an unprotected person with fewer assumptions," says Gholamhossein Bagheri, who as a research group leader at the Max Planck Institute for Dynamics and Self-Organization who is the lead author of the current study.
