The WHO director-general Tedros Adhanom Ghebreyesus said on June 5 that “in light of evolving evidence, WHO advises that governments should encourage the general public to wear masks where there is widespread transmission and physical distancing is difficult, such as on public transport, in shops or in other confined or crowded environments.” The global body said new information showed face-masks could provide “a barrier for potentially infectious droplets”.
Face-masks are now becoming an integral part of our dress code, for sure. While the West wasn’t very comfortable with the idea of face-masks in the pre-COVID-19 era, East Asians were more welcoming of them. Some prefer to see the masking culture in China, Japan and South Korea as an influence of Taoism and the precepts of traditional medicine. The scientific motivation to use face-masks to resist contagion is in fact quite old itself. Masks became a marker of China’s medical modernity through a Malayan-Chinese doctor named Wu Lien-teh. During a pneumonic plague in Manchuria in 1910, Dr Lien-teh recognised that healthy people were infected through droplets from those who were sick, and he promoted the use of specially manufactured gauze masks among Chinese and foreign medical staff during the epidemic, and also among patients and suspects.
Face-masks for containment and mitigation measures during epidemics were also widely used during the 1918 Spanish flu pandemic in different parts of the world. The Japanese used face-masks during the Great Kanto Earthquake of 1923 and the global flu pandemic of 1934. The mask-wearing culture to protect contagion in South and Southeast Asian countries received a boost during the 2002-2003 SARS epidemic, which severely affected this part of the world.
In April 2020, researchers published a paper showing that face-masks completely eliminate the emission of particles. Seven years ago, another group of researchers had shown that cloth masks filtered viral particles during coughing at about 50-100% of the filtration efficiency of surgical masks, depending on the fabric. They noted that cloth masks also had an absolute filtration efficiency of 50-70%, and about 70-80% for oral bacteria.
In this context, it might be helpful to discuss some scientific studies to understand how and to what extent face-masks can be effective in restricting contagion. A multidisciplinary group convened by the UK Royal Society called DELVE — Data Evaluation and Learning for Viral Epidemics – recently published a report. In it, the authors observed that the use of face-masks “could reduce onward transmission [of COVID-19] by asymptomatic and pre-symptomatic wearers if widely used in situations where physical distancing is not possible or predictable, contrasting to the standard use of masks for the protection of wearers.”
In a paper published on April 30, two authors from Australia described a systematic review of the efficacy of face-masks against coronaviruses and other respiratorily transmissible viruses for the community and healthcare workers and sick patients. The authors included 19 randomised controlled trials in their analysis: eight in community settings, six in healthcare settings and five as source control. In the community, masks appeared to be more effective than hand hygiene alone, and both together were more protective. The authors concluded, “Universal face-mask use is likely to have the most impact on epidemic growth in the community, given the high risk of asymptomatic and pre-symptomatic transmission.”
In a more recent paper, published on June 1, a group of scientists mostly from McMaster University, Canada, undertook out a systematic review and meta-analysis for the effects of physical distancing, face-mask use and eye protection on prevention of person-to-person transmission of the novel coronavirus. Their analysis was based on 172 observational studies conducted in 16 countries on six continents, in health-care and non-health-care settings, with 25,697 patients with coronavirus diseases like COVID-19, SARS and MERS. They found that physical distancing of one metre or more was associated with a much lower risk of infection, as was the use of face-masks (including N95 respirators, surgical masks and similar), and eye protection (e.g., goggles or face-shields).
These researchers also compared the data pertaining to physical distancing of more and less than one metre from 38 studies, with a total sample size of 18,518. They noted that the chances of a viral infection or transmission was 12.8% for shorter distances and 2.6% for longer distances. Finally, they concluded that a physical distance of more than one metre probably results in a large reduction in the chances of developing an infection, and for every one metre of distancing, the relative effect could increase by 2.02-times.
Next, they studied the effects of using face-masks relative to not using them based on 10 adjusted studies and 29 unadjusted studies with a total sample size of 12,817. The chance of a viral infection was 17.4% with no face-mask, and 3.1% with the use of face-masks. So the authors concluded that the use of medical or surgical face-masks could substantially reduce the incidence of infections, and that N95 respirators could be associated with a larger reduction of risk relative to the use of surgical or similar masks.
Four of their studies included in the analysis involved COVID-19 patients – all in healthcare settings – and only one out of 1,659 individuals developed COVID-19 despite using face-masks. Some 132 out of 4,270 who didn’t use face-masks tested positive. The data pertaining to 3,713 individuals in 13 unadjusted studies on eye protection versus no eye protection shows that 16% of those who didn’t protect their eyes developed an infection versus 5.5% of those who did.
Thus, while the lockdown cannot continue forever, and every country must open up their respective economies at some point, we must protect ourselves as much as is reasonably possible. Physical distancing and the use of face-masks should be the new normal if it already isn’t. Who knows, whenever you step out hence, and even after the pandemic has concluded, you may try to remember where you kept your wallet, your spectacles, and then your mask.
Atanu Biswas is a professor of statistics at the Indian Statistical Institute, Kolkata.