Face Masks Effectively Limit the Potential for SARS-CoV-2 Transmission
Airborne transmission by droplets and aerosols is important for the spread of the virus. Face masks are a well-established preventive measure, but their effectiveness in reducing SARS-CoV-2 transmission is still under debate. Variation in mask effectiveness can be explained by different regimes of viral abundance and is related to the population average probability of infection and the number of reproductions. in the case of SARS-CoV-2, viral abundance in infected individuals can vary by orders of magnitude. Most environments and contacts are found to be under conditions of low viral abundance (virus-limited) where surgical masks are effective in preventing the spread of the virus. In indoor environments where viruses may be abundant, such as medical centers and hospitals, more sophisticated masks and other protective equipment are required.
Yafang Chen, Nanma, Christian Witt, Steffen Rapp, Philip S. Wild, Meinrat O. Andreae, Ulric Poskul, Hang Su, Science May 20, 2021 eabg6296
DOI: 10.1126 / science.abg6296
Commentary
In this study, we want to understand and quantify the impact of the probability of infection to assess the effectiveness of masks P inf file, it is assumed that every inhaled single virus has a chance to infect a person, P inf file, was done to calculate in a single hit model of infection.
According to their analysis, they focused on respiratory particles and droplets with a diameter of less than 100 μm, explaining that due to rapid gravitational settling, respiratory droplets greater than 100 μm would be removed from the air within seconds, but would still reach the upper respiratory tract of a person in close contact and could cause infection by carrying a very large amount of virus in large quantities.
For example, at a viral load of 10 8 per milliliter of respiratory fluid, a one millimeter droplet could carry up to 50,000 viruses. This explanation is realistic and turns out to be higher than the estimated infectious dose of SARS-CoV-2. However, this large droplet is removed by a simple mask efficiently, which is supposed to highlight the importance and effectiveness of face masks in preventing infection.
Since this is highly size-dependent, it is recommended that the diameter range be explicitly specified to avoid ambiguity when describing fine respiratory aerosol particles and airborne transmission by large droplets.
In summary, mask precautions in this setting are important as a precaution against airborne viruses such as SARS-CoV-2.
Often in the media, when we see images verifying the effectiveness of masks, we see respiratory particles exhaled from conversations, coughing, etc. We may worry that masks with limited filtration efficiency (30-70%, etc.) will not be able to prevent these particles from entering the air. The observed effectiveness of face masks in preventing the spread of P infiltrate regime and COVID-19, which is an area restricted to viruses, is illustrated by wearing a mask that can keep the number of inhaled viruses to a low, and indeed most environments.
However, it is explained that under different circumstances (space, viral load) than in this experiment, further measures such as highly efficient masks and efficient ventilation are needed. In other words, the effectiveness of masks depends on the environment, and the environment in which higher-efficiency masks are required depends on conditions such as high virus levels and inadequate ventilation, so this explanation does not deny the effectiveness of face masks alone.
If you want to know the detailed experimental conditions, click here.
