Better-fitting masks provide better protection against COVID

New research shows that 9.8 feet (3 meters) of social distancing is not enough to provide protection against Covid-19. Even at this 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% certainty.

This is the bad news.

The good news is that if both people wear properly fitting medical masks, or better yet, N95 or FFP2 masks, the risk drops dramatically.

The researchers studied how well the masks protect under which conditions of wearing. In the process, the researchers determined the maximum risk of infection for many situations and took into account several factors not included in similar studies. The in-depth study published on December 7 in the Proceedings of the National Academy of Sciences (PNAS).

The team at the Max Planck Institute for Dynamics and Self-Organization in Göttingen, Germany, which includes Eberhard Bodenschatz, Assistant Professor of Physics in the Faculty of Arts and Sciences and Aerospace and Mechanical Engineering at the Faculty engineering, was surprised at the ease of transmission of the coronavirus.

“We would not have thought that at a distance of several meters it would take such a short time for the infectious dose to be absorbed by the breath of a virus carrier,” said Bodenschatz, director of the Institute. Max Planck.

At this distance, the researchers found that the exhaled air had already spread in a cone shape through the air; infectious particles are diluted accordingly. In addition, particularly large and therefore virus-rich particles fall to the ground after only a short distance in the air.

“In our study, we found that the risk of infection without wearing masks is extremely high after just a few minutes, even at a distance of three meters, if those infected have the high viral load of the delta variant of Sars- CoV-2 virus, ”Bodenschatz said. And such encounters are inevitable in schools, restaurants, clubs or even outdoors.

Nevertheless, medical masks or FFP2 provide effective protection. The study confirms that FFP2 or N95 masks are particularly effective at filtering infectious particles from the air – especially if the masks are sealed to the face as tightly as possible. If both the infected person and the uninfected person wear well-fitting FFP2 masks, the maximum risk of infection after 20 minutes is little more than one in 1000, even at the shortest distance. If their masks are poorly fitted, the likelihood of infection increases to around 4%. If both wear properly fitted medical masks, the virus is likely to be transmitted within 20 minutes with a maximum chance of 10%. The study also supports the intuitive hypothesis that for effective protection against infection, the infected person in particular should wear a mask that filters as best as possible and fits tightly to the face.

The probabilities of infection determined by Max Planck’s team indicate the upper limit of risk in each case. In everyday life, the real probability of infection is certainly 10 to 100 times lower. “This is because the air coming out of the mask at the edges is diluted, so you don’t get all the unfiltered breathable air,” Bodenschatz said. “But we assumed this because we can’t measure in all situations how much breathable air from a mask wearer reaches another person, and because we wanted to calculate the risk as carefully as possible.

“Under these conditions, if even the greatest theoretical risk is small, then you are on the very safe side under real conditions.”

For comparative value without the protection of a mask, however, the safety pad turns out to be much smaller. “For such a situation, we can determine the viral dose inhaled by an unprotected person with fewer assumptions,” said Gholamhossein Bagheri, research group leader at the Max Planck Institute and lead author of the study.

In their calculations of the risk of infection, the researchers took into account a number of factors that had not previously been included in comparable studies, including how an ill-fitting mask weakens protection and how this can be avoided.

“The materials of FFP2 or KN95 masks, but also some medical masks, filter extremely effectively,” Bagheri said. “The risk of infection is then dominated by the air coming out and entering the edges of the mask.” This happens when the edge of the mask is pulled away from the face.

In elaborate experiments, Bagheri, Bodenschatz and their team measured the size and amount of respiratory particles that pass past the edges of masks that fit differently.

“A mask can be perfectly tailored to the shape of the face if you bend its metal strap into a rounded W before putting it on,” Bodenschatz said. “Then the infectious aerosol particles no longer get past the mask – and the glasses don’t fog up either. “

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