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Face Masks Are Effective in Lowering the Reproductive Number of COVID-19

Face Masks Are Effective in Lowering the Reproductive Number of COVID-19

Face Masks Are Effective in Lowering the Reproductive Number of COVID-19

Face Masks Are Effective in Lowering the Reproductive Number of COVID-19

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Face masks are one of the simplest, easiest to use, and most effective measures to prevent airborne infectious respiratory diseases. Nevertheless, their effectiveness against the transmission of SARS-CoV-2 has been discussed and questioned many times. Some previous studies have shown that masks are ineffective under certain conditions. Others found it to be very effective. A coherent justification and clarification of the apparent contradictions have so far been missing.

Researchers from the Max Planck Institute for Chemistry (MPIC), the University Medical Center of Johannes Gutenberg University Mainz and the Charité University Medical Center Berlin, together with partners from China and the USA, have now clarified how the effectiveness of face masks depends on various environmental conditions and has a population-wide impact on the course of the COVID-19 pandemic. To do this, they used a large number of observational data as well as a novel approach to calculating the average virus load and its distribution in the population. 

Most of the time, even simple surgical masks are effective

“Usually only a small proportion of the droplets and aerosol particles exhaled by humans contain viruses. The virus concentration in the air is usually so low that even simple surgical masks are very effective in curbing the spread of COVID-19, ”explains Yafang Cheng, head of a Minerva research group at the MPIC. "Our approach allows detailed calculations of population mean values ​​and explains why regions where a higher proportion of the population wears masks have the pandemic better under control."

In virus-rich indoor areas with a high probability of infection, however, masks with higher effectiveness (N95 / FFP2) and other protective equipment are required to prevent airborne transmission. Because the effectiveness of face masks depends heavily on the virus concentration, it is important to combine masks with other protective measures in order to keep the chances of infection low.

"The combination of high-quality masks with other protective measures such as ventilation and keeping a safe distance is particularly important for hospitals, medical centers and other indoor spaces where high-risk patients can encounter high virus concentrations," says Christian Witt, head of the pneumology research department at Charité - Universitätsmedizin Berlin. "Masks will remain an important protective measure against SARS-Cov-2 infections - even for vaccinated people, especially if the vaccination protection wears off over time."

The approach can be used to assess the protection against more infectious mutants

“Our method relates the effect of masks and other protective measures to the likelihood of infection and the number of reproductions. The approach and our results are applicable to a wide variety of respiratory viruses such as corona, rhino and influenza viruses and the corresponding diseases. They can also be used to assess the effectiveness against new and more infectious mutants of SARS-CoV-2, ”says Hang Su, research group leader at the MPIC. “Our study also explains why the aerosol transmission of viruses does not necessarily lead to the very high reproductive numbers that have been observed in measles. Even with relatively low chances of infection and reproductive numbers, the transmission of an infectious disease through the air cannot be ruled out. "

The study, now published in the science magazine Science, also shows that masks can only effectively reduce the number of reproductions for COVID-19 if as many people as possible use them correctly. In order to reduce the reproductive number from about three, as originally observed, to below one, at least 60 to 70 percent of people would have to use surgical masks correctly. With N95 / FFP2 masks it would be around 40 percent. With more infectious variants of SARS-CoV-2, the rates would have to be correspondingly higher.

"We are convinced that the mechanistic findings and quantitative results obtained in our study represent a scientific breakthrough that will help bring the debate about the usefulness of masks to a close and efficiently contain the COVID pandemic," summarizes Ulrich Pöschl, head of the department Multiphase chemistry at the Max Planck Institute for Chemistry in Mainz.

 Cheng Y, Ma N, Witt C, et al. Face masks effectively limit the probability of SARS-CoV-2 transmission. Science. 2021. doi: 10.1126/science.abg6296

This article has been republished from the following materials. Note: material may have been edited for length and content. For further information, please contact the cited source.