Science | Dispelling doubts, Jinan University and other units cooperated, Su Hang/Cheng Yafang found that wearing masks effectively limited the spread of the new crown virus

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Due to the rapid increase in new cases of iNature, the 2019 Coronavirus Disease (COVID-19) quickly attracted global attention, and the pathogen was identified as SARS-CoV-2.

As of now (May 18, 2021), according to real-time statistics released by Johns Hopkins University, the cumulative number of confirmed cases of new coronary pneumonia worldwide has exceeded 164.
04 million, and the death toll has reached 3.
4 million.

These figures are updated every day and are expected to increase further.

Masks are an effective preventive measure, but their effectiveness in mitigating the spread of SARS-CoV-2 is still controversial.

 On May 20, 2021, the Max Planck Institute of Chemistry, Jinan University, Shanghai Research Institute of Environmental Sciences, University of California San Diego and many other units cooperated.
Suhang and Cheng Yafang jointly published a newsletter titled "Face masks" on Science Online Effectively limit the probability of SARS-CoV-2 transmission" research paper, the study found that the difference in the efficacy of masks can be explained by different mechanisms of virus abundance, and is related to the average infection probability of the population and the number of reproduction.

 For SARS-CoV-2, the viral load of an infected person can vary by several orders of magnitude.

The study found that most of the environment and contact conditions are under the condition of low virus abundance (virus restriction), and surgical masks can effectively prevent the spread of the virus.

In indoor environments (including medical centers and hospitals) that may be rich in viruses, more advanced masks and other protective equipment are required.

Masks combined with other preventive measures, such as ventilation and evacuation, are particularly effective in preventing the spread of the new crown.

Airborne transmission is one of the main ways of respiratory viruses, including SARS-CoV-2.

The wearing of masks is widely advocated to reduce transmission.

Masks are believed to protect people in two ways: source control, which reduces the emission and spread of respiratory viruses through droplets and aerosols in the air; and the protection of the wearer, reduces the inhalation of respiratory viruses in the air.

However, the effectiveness of masks is still under debate.

Compared with N95/FFP2 respirators with very low particle permeability (approximately 5%), surgical masks and similar masks have higher permeability and greater variation (approximately 30-70%).

In view of the fact that a large number of particles are emitted when breathing, especially when sneezing or coughing, a large number of breathing particles may penetrate the mask, which is one of the main reasons for doubts about its anti-infection efficacy.

In addition, randomized clinical trials have shown inconsistent or uncertain results, and some studies have reported that the benefits of using masks are small or ineffective.

Therefore, surgical masks and similar masks are generally considered ineffective.

On the other hand, observational data show that areas with a higher proportion of people wearing masks can better control COVID-19.

So, how to explain these opposite results and obvious contradictions? Here, the study established a quantitative model of airborne virus exposure, which can explain these opposite results and provide a basis for quantifying the efficacy of masks.

The study shows that the efficacy of masks depends largely on the abundance of viruses carried.

Based on the direct measurement results of SARS-CoV-2 in air samples and the probability of infection at the population level, the study found that the abundance of the virus in most environments is low enough, so masks can effectively reduce airborne transmission.

Reference message: https://science.
sciencemag.
org/content/early/2021/05/19/science.
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