Facial masks effectively limit SARS-CoV-2 transmission


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“Don’t forget about the mask,” although most people today follow this advice, professionals express different opinions about the effectiveness of facial masks. An international team led by researchers at the Max Planck Institute for Chemistry in Mainz, Germany, has now used observational data calculations and models to answer open-ended questions. The study shows under what conditions and how masks actually reduce the individual and population’s risks of being infected with COVID-19 and help mitigate the crown pandemic. In most environments and situations, even simple surgical masks effectively reduce the transmission of SARS-CoV-2 and the effective reproduction number of COVID-19. However, in environments with potentially high concentrations of viruses in the air, such as medical facilities and densely occupied indoor spaces, masks with a higher filtration efficiency (N95 / FFP2) should be used and combined. with other protection measures such as intensive ventilation.

Facial masks are one of the simplest, easiest to use, and most effective measures against the airborne transmission of infectious respiratory diseases, but their usefulness against COVID-19 is still under debate. Some previous research found that apparently masks were not effective under certain conditions. Others found high efficacy, but no conclusive explanation of the apparent contradictions and inconsistencies had been given.

Researchers at the Max Planck Institute for Chemistry (MPIC), the Medical Center of Johannes Gutenberg University in Mainz and the Charité – Universitätsmedizin Berlin together with partners from China and the United States used observational data and a new quantitative model of exposure to airborne virus as the effectiveness of masks depends on the characteristic regimes of concentration of airborne viruses.

In most situations, even simple surgical masks are effective

“For SARS-CoV-2 airborne transmission, we find that typically only a small fraction of exhaled respiratory particles contain viruses. Most environments and contacts are in virus-limited conditions, where face masks, including masks, simple surgical procedures have a high efficacy in preventing the spread of COVID-19, ”explains Yafang Cheng, head of a Minerva research group at MPIC. “Our study provides a mechanized and detailed understanding of the average effectiveness of the population mask, which explains why regions with a higher percentage of the population wearing masks have better control of the pandemic.”

However, in virus-rich indoor environments with a high probability of infection, more advanced masks (N95 / FFP2) and other protective equipment are needed to prevent airborne transmission. The strong reliance on the effectiveness of masks on the concentration of viruses in the air highlights the importance of combining masks with other protective measures such as ventilation and spacing to keep the likelihood of infection low.

“The combination of high-efficiency masks with other protective measures is particularly important for hospitals, medical centers and other indoor environments, where high-risk patients can find high concentrations of viruses,” says Christian Witt, head of the Charité’s pulmonology research area. – Universitätsmedizin Berlin. “Masks will continue to be an important measure of protection against SARS-Cov-2 infection, even for vaccinated people, especially when the protection provided by vaccination decreases over time.”

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

“Our approach and results of relating the effectiveness of protective measures to the likelihood of infection and the basic number of reproductions are applicable to a wide range of viruses and respiratory diseases, including coronaviruses, rhinoviruses, and influenza. They can also be used to evaluate the effectiveness of masks and other preventive measures against new and more infectious SARS-CoV-2 mutants. “Says Hang Su, leader of the MPIC research group. “Our research also shows that aerosol transmission does not necessarily lead to a very high reproduction number, as observed for measles, and that a relatively low reproduction number does not rule out airborne transmission.”

In addition, the study demonstrates the importance of high compliance and the correct use of masks to ensure their effectiveness in reducing the number of COVID-19 reproductions. To reduce the reproduction number by 33, as originally observed, below 1, at least 60–70% compliance would be required for surgical masks (4040% for N95 / FFP2 masks). Higher compliance rates would be required for more infectious variants of SARS-CoV-2, which stresses that masks should be combined with other protective measures such as ventilation and spacing to efficiently reduce the chances of infection and the number of reproduction.

“Our study quantitatively explains why and how they are highly effective in virus-limited environments and less effective in virus-rich environments, both at the individual level and at the middle level of the population, related to the observed infection rates and the number of effective reproduction. This has not been achieved before and is essential to overcome previous and inconclusive results, arguments and discussions. We are confident that the mechanistic views and quantitative results obtained in our study constitute a scientific advance that will help resolve the ongoing debate about the usefulness of and promote efficient mitigation of the COVID pandemic, ”sums up Ulrich Pöschl, director of the MPIC Multiphasic Chemistry Department.

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More information:
Yafang Cheng et al, Facial masks effectively limit the likelihood of SARS-CoV-2 transmission, Science (2021). DOI: 10.1126 / science.abg6296

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Max Planck Society

Citation: Facial masks effectively limit the transmission of retrieved SARS-CoV-2 (2021, May 21) on May 22, 2021 at https://medicalxpress.com/news/2021-05-masks-effectively-limit-sars -cov-transmission.html

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