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A well-fitting FFP2 mask provides almost 100 percent protection against a COVID-19 infection

Masks that do not close tightly at the edges let air in and out. But even poorly fitting masks significantly reduce the risk of infection. | Ⓒ Birte Thiede / MPIDS

How well can masks protect?

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Even at a distance of three meters, it takes less than five minutes for an unvaccinated person standing in the breath of a Covid-19-infected person to become infected, with almost 100 percent certainty. However, if both people wear well-fitting medical, or better yet, FFP2 masks, the risk drops dramatically. This is shown by a study by the Max Planck Institute for Dynamics and Self-Organization in Göttingen.​ ​

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The Göttingen research team was surprised at how great the risk is of contracting the coronavirus without a mouth and nose protection. "We would not have thought that at a distance of several meters it would take so little time for the infectious dose to be absorbed from the breath of a virus carrier," says Eberhard Bodenschatz, Director at the Max Planck Institute for Dynamics and Self-Organization and Principal Investigator at the DZHK. 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 meters, if the infected persons have the high viral load of the delta variant of the Sars-CoV-2 virus," says Eberhard Bodenschatz. Such encounters are unavoidable in schools, restaurants, clubs or outdoors.

Well-fitting FFP2 masks reduce the risk to at least the per mil range

In the comprehensive study,  by a team from the Max Planck Institute for Dynamics and Self-Organization in Göttingen, it was investigated to what extent masks protect under which wearing conditions. FFP2 or KN95 masks are particularly effective at filtering infectious particles out of the air we breathe - especially if they are as tightly sealed as possible at the face. If both the infected and the non-infected person wear well-fitting FFP2 masks, the maximum risk of infection after 20 minutes is barely more than one per thousand, even at the shortest possible distance. If their masks are badly fitted, the likelihood of infection increases to around four percent. "A mask can be perfectly adapted to the shape of the face if you bend its metal bracket into a rounded W before putting it on," says Eberhard Bodenschatz. "Then the contagious aerosol particles can no longer get past the mask and glasses no longer fog up."

If both of them wear well-fitted surgical masks, the virus will be transmitted within 20 minutes with a probability of no more than ten percent. The investigation also confirms the assumption that for effective protection against infection, the infected person in particular should wear a mask that filters as well as possible and tightly fits.

Without a mask, the risk of infection is almost 100 percent

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“ Without a mask, the risk of being infected within a few minutes is almost 100 percent, even from a distance of three meters.

Publication: Gholamhossein Bagheri, Birte Thiede, Bardia Hejazi, Oliver Schlenczek and Eberhard Bodenschatz. An upper bound on one-to-one exposure to infectious human respiratory particles. Proceedings of the National Academy of Sciences, December 7, 2021. https://doi.org/10.1073/pnas.2110117118

Source: Max-Planck-Institut für Dynamik und Selbstorganisation