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Why does the spread of COVID-19 vary greatly in different countries? Revealing the efficacy of face masks in epidemic prevention.

  • Wei, Jincheng1
  • Guo, Shurui1
  • Long, Enshen1
  • Zhang, Li2
  • Shu, Bizhen3
  • Guo, Lei1
  • 1 MOE Key Laboratory of Deep Earth Science and Engineering, College of Architecture and Environment, Sichuan University, Chengdu, China. , (China)
  • 2 Department of Solid Waste Treatment Technology, Sichuan Environmental Protection Key Laboratory of Pollution Control for Heavy Metals, Sichuan Academy of Environmental Sciences, Chengdu, China. , (China)
  • 3 Key Laboratory of Birth Defects and Related Diseases of Women and Children, West China Second Hospital of Sichuan University, Chengdu, China. , (China)
Published Article
Epidemiology and Infection
Cambridge University Press
Publication Date
Jan 14, 2021
DOI: 10.1017/S0950268821000108
PMID: 33441205


The severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) is highly contagious, and the coronavirus disease 2019 (COVID-19) pandemic caused by it has forced many countries to adopt 'lockdown' measures to prevent the spread of the epidemic through social isolation of citizens. Some countries proposed universal mask wearing as a protection measure of public health to strengthen national prevention efforts and to limit the wider spread of the epidemic. In order to reveal the epidemic prevention efficacy of masks, this paper systematically evaluates the experimental studies of various masks and filter materials, summarises the general characteristics of the filtration efficiency of isolation masks with particle size, and reveals the actual efficacy of masks by combining the volume distribution characteristics of human exhaled droplets with different particle sizes and the SARS-CoV-2 virus load of nasopharynx and throat swabs from patients. The existing measured data show that the filtration efficiency of all kinds of masks for large particles and extra-large droplets is close to 100%. From the perspective of filtering the total number of pathogens discharged in the environment and protecting vulnerable individuals from breathing live viruses, the mask has a higher protective effect. If considering the weighted average filtration efficiency with different particle sizes, the filtration efficiencies of the N95 mask and the ordinary mask are 99.4% and 98.5%, respectively. The mask can avoid releasing active viruses to the environment from the source of infection, thus maximising the protection of vulnerable individuals by reducing the probability of inhaling a virus. Therefore, if the whole society strictly implements the policy of publicly wearing masks, the risk of large-scale spread of the epidemic can be greatly reduced. Compared with the overall cost of social isolation, limited personal freedoms and forced suspension of economic activities, the inconvenience for citizens caused by wearing masks is perfectly acceptable.

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