The increasing polarised and
politicised views 1 on whether to wear masks in public during the current COVID-19 crisis hides a bitter truth on the state of contemporary research and the value we pose on clinical evidence to guide our decisions.
In 2010, at the end of the last influenza pandemic, there were six published randomised controlled trials with 4,147 participants focusing on the benefits of
different types of masks. 2 Two were done in healthcare workers and four in family or student clusters. The face mask trials for influenza-like illness (ILI) reported poor compliance, rarely reported harms and revealed the pressing need for future trials.
Despite the clear requirement to carry out further large, pragmatic trials a decade later,
only six had been published: five in healthcare workers and one in pilgrims. 3 This recent crop of trials added 9,112 participants to the total randomised denominator of 13,259 and showed that masks alone have no significant effect in interrupting the spread of ILI or influenza in the general population, nor in healthcare workers.
The design of these twelve trials differed: viral circulation was usually variable; none had been conducted during a pandemic. Outcomes were defined and reported in seven different ways, making comparison difficult. It is debatable whether any of these results could be applied to the transmission of SARs-CoV-2.
Only one randomised trial (n=569) included cloth masks. This trial found ILI rates were 13 times higher in Vietnamese hospital workers allocated to cloth masks compared to medical/surgical masks, RR 13.25, (95%CI 1.74 to 100.97) and over three times higher when compared to no masks,* RR 3.49 (95%CI 1.00 to 12.17). 4
It would appear that despite two decades of pandemic preparedness, there is considerable uncertainty as to the value of wearing masks. For instance, high rates of infection with cloth masks could be due to harms caused by cloth masks, or benefits of medical masks. The numerous systematic reviews that have been recently published all include the same evidence base so unsurprisingly broadly reach the same conclusions. 2 However,
recent reviews using lower quality evidence found masks to be effective. Whilst also recommending robust randomised trials to inform the evidence for these interventions. 5
Many countries have gone onto mandate masks for the public in various settings. Several others – Denmark, and Norway – generally do not.
Norway’s Institute for Public Health reported that if masks did work then any difference in infection rates would be small when infection rates are low: assuming 20% asymptomatics and a risk reduction of 40% for wearing masks, 200 000 people would need to wear one to prevent one new infection per week. 6
[The text continues on to discuss the need for more trials, and lists presently-ongoing trials]
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