Background and Evidence for Mask-Wear

Covid-19 infection has been shown to produce pneumonia-like symptoms that go on to aggravate damage to the lungs and heart, as the disease progresses. Elevated markers for inflammation, cardiac damage and low oxygen levels are observed in critically ill individuals who often require mechanical ventilation.

Individuals of advanced age (>65 yrs), or those with pre-existing medical conditions including cardiovascular diseases, obesity, diabetes and respiratory illness, or compromised immunity, are thought to be at particular risk from developing the severe forms of the disease that require hospitalisation. Men are also disproportionately affected [Rong-Hui Du et al., 2020; Petrilli et al., 2020].

The SARS-Cov-2 virus has been confirmed as gaining entry to cells in the respiratory system by binding to the Angiotensin-Converting Enzyme II (ACE-2) receptor [Zhou P, et al., 2020]. As mentioned, one potential mechanism is thought to be via respiratory droplets inhalation. This term refers to oral fluid that is >20 microns in size, that will eventually drop to the ground through gravity over a short distance (~2M).

Respiratory droplets are commonly thought to come from coughing and sneezing, but there is evidence that sizeable fluid droplets can be generated by talking, demonstrated in a recent study [Anfinrud P. et al., 2020]. To compound matters for transmission, viral load is thought to be highest in asymptomatic and pre-symptomatic individuals, who are therefore thought to be highly contagious [He, X et al., 2020; Zou, L. et al., 2020].

RM Medical - A Complete Guide To Face Mask Use in Clinical and Public Settings

Aerosols are also generated through similar mechanisms to respiratory droplets, containing significantly smaller particles, (in the single micron range), suspended in gas. These can travel much further, and studies have linked them to infection, especially in enclosed spaces where they are not readily dispersed. As such, there is an increased risk for the spread of contagion indoors, for example on public transport, in shops, hospitality venues, certain construction sites and factory environments. Exactly what proportion of Covid-19 infections are attributable to aerosol or respiratory droplet transmission remains to be calculated [Meselson, M. 2020; van Doremalen, N. et al., 2020]

Recent research published in Proceedings of the National Academy of Science, supports airborne transmission, via inhalation of virus-bearing aerosols, as a dominant route for the transmission of Covid-19 [[Zhang et al., 2020]. In this study, Dr. Renyi Zhang and colleagues from Texas A&M University used statistical modelling of infection rates in pandemic epicentres. They calculated that between April 17 to May 9 2020, 66K infections in New York were prevented, also a further 78K were mitigated in Italy over a similar time period, only once face mask use was made compulsory.

‘wearing of face masks in public corresponds to the most effective means to prevent inter-human transmission of Covid-19’ [Zhang, R et al., 2020]

They emphasised that considerably more infections could have been prevented worldwide if face masks were made mandatory from the start of the pandemic. Moreover, global policies for social distancing, quarantine, and isolation had minimized contact transmission, and not aerosol transmission, allowing infection to spread. They concluded that ‘wearing of face masks in public corresponds to the most effective means to prevent inter-human transmission of Covid-19’. [Zhang et al., 2020].

In a recent joint epidemiological study between the University of Greenwich and the University of Cambridge, two different models were used to assess the effectiveness of facemasks on the current pandemic [Stutt, OJR. et al., 2020]. The best outcomes were achieved when masks were worn all the time in public (even after the onset of symptoms), by a high proportion of the population and the efficacy of the mask was high (>95% – of the type provided by N95 respirator masks). They also noted that 100% adoption of facemasks, even with on/off lock-down periods could prevent subsequent waves of infection, and furthermore, result in the pandemic dying out (R = <1).

‘swiftly increase the availability of medical standard surgical, or N95 respirators to the public.’ [Stutt, OJR. et al., 2020]

In their concluding remarks, the authors cited that the UK should take action to provide clear instructions on the fabrication and safe use of home-made masks. Furthermore, policy makers should ‘swiftly increase the availability of medical standard surgical, or N95 respirators to the public.’ The latter are designed to give a very close facial fit and highly efficient filtration of 0.3 μm airborne particles (we discuss this in more detail below). Interestingly, many countries that have introduced mask wearing early on in their response to the pandemic have seen flatter curves for the rate of infection. For example in Europe – Germany encourages non-medical mask wearing (to avoid depleting supplies for health workers) and fines are issued for non-compliance, or in Asia — countries like South Korea and Taiwan, where respirator mask use, (Korea 1st class masks and N95 masks respectively), has been enforced with distribution through pharmacies.

There may of course be other contributory factors to lower infection rates due to differences of approach in the health response to Covid-19 — testing, tracing and tracking individuals rigorously is one such example. However, it is notable that this applies to several countries and territories with early use of masks as part of official government or practice policy [Longrich N, et al 2020].


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  • He, X., Lau, E.H.Y., Wu, P. et al. 2020. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nat Med. 26, 672–675.
  • Longrich N, Sheppard S. 2020. Public use of face masks to control the coronavirus (SARS-Cov-2) pandemic: a review of theory and evidence. Preprints. 2020040021Meselson, M. 2020. Droplets and Aerosols in the Transmission of SARS-CoV-2. N Engl J Med. 382:2063 DOI: 10.1056/NEJMc2009324
  • Rong-Hui Du et al., 2020. Predictors of Mortality for Patients with COVID-19 Pneumonia Caused by SARS-CoV-2: A Prospective Cohort Study European Respiratory Journal; DOI: 10.1183/13993003.00524-2020
  • Stutt ROJ, Retkute R, Bradley M, Gilligan CA and Colvin J; A modelling framework to assess the likely effectiveness of facemasks in combination with ‘lock-down’ in managing the COVID-19 pandemic. Proceedings of the Royal Society A. 10 June 2020
  • Zou L, Ruan F, Huang M, et al. 2020. SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. N Engl J Med. 382(12):1177-1179. doi:10.1056/NEJMc2001737
  • Zhang R, Li Y, Zhang AL, Wang Y, Molina MJ. Identifying airborne transmission as the dominant route for the spread of COVID-19 [published online ahead of print, 2020 Jun 11]. Proc Natl Acad Sci U S A. 2020;202009637. doi:10.1073/pnas.2009637117