Do face masks stop spread of coronavirus?

Prof Asif Ahmed discusses...

Rate of mask usage by Hong Kong people since the start of the local epidemic in January has meant less cases of COVID19. Studies found that more than 95% of people in Hong Kong used face masks (Cheng VC et al, J Infect), which directly observed 10,050 people during their morning commute over 3 days in April. By wearing masks, people not only protect themselves and their families, but also protect those among us who don't or can't wear masks. The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2 was published by Cheng VC and colleagues in Journal of Infection, 2020.

Some modelling data suggests that influenza outbreaks can be stopped if 80% of people wear a mask (Yan J et al, Risk Anal, 2019). The 'herd masking threshold' for stopping COVID-19 spread is unknown, but Hong Kong has probably exceeded it. This may explain why wearing a mask by all is a standard practice in Hong Kong and in the Czech Republic, who had a low death toll.

We risk inhaling “micro-droplets” of virus that hang around floating long after the person who had coughed or sneezed has gone. A study done by Kyoto Institute of Technology in Japan found masks reduce emissions of infected saliva and droplets from mild COVID19 cases.

Second Wave of COVID-19 and history’s lesson is illustrated below. The Stay-At-Home order has started to end not because there is an end of the #pandemic. It just means that the hospitals now have greater capacity to take in patients into their ICU. It is of paramount important for all of us to keep social distancing to stay safe. The community-wide benefit is likely to be greatest when face masks are used (Eikenberry SE et al 2020). It may help to keep everyone safer until we have a safe drug to prevent or treat Covid-19 or a successful and safe vaccine is available.

The MedShr team would like to thank Prof Asif Ahmed for the text and images in this post.

Published by Dr Rachel Coles on his behalf, on 28th May 2020.


Cheng VCC, Wong SC, Chuang VWM, So SYC, Chen JHK, Sridhar S, To KKW, Chan JFW, Hung IFN, Ho PL, Kwok-Yung Yuen KY (2020).  The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2. J Infect. 2020 Apr 23 doi: 10.1016/j.jinf.2020.04.024 [Epub ahead of print]


Yan J, Guha S, Hariharan P, Myers M (2019). Modeling the Effectiveness of Respiratory Protective Devices in Reducing Influenza Outbreak. Risk Anal;39(3):647-661. doi: 10.1111/risa.13181.


Tracht SM, Del Valle SY, Hyman JM (2020). Mathematical modeling of the effectiveness of facemasks in reducing the spread of novel influenza A (H1N1). PLoS One. 5(2):e9018. doi: 10.1371/journal.pone.0009018.


Eikenberry SE, Mancuso M, Iboi E, Phan T, Eikenberry K, Kuang Y, Kostelich E, Abba B. Gumel AB (2020). To mask or not to mask: Modeling the potential for face mask use by the general public to curtail the COVID-19 pandemic.  Infect Dis Model. 5: 293–308. doi: 10.1016/j.idm.2020.04.001





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