Revisiting the evidence for physical distancing, face masks, and eye protection

Derek Chu and colleagues reported that face mask wearing in hospitals and health-care settings reduces risk of respiratory infection.¹ Surprisingly, this recommendation was extended to the general population. Summary estimates were calculated using results of three severe acute respiratory syndrome studies, of which only two yielded statistically significant results. The first study was done in households, a situation that is similar to a health-care setting.² The second was a case-control study in the general population where infected and uninfected individuals were asked via telephone interviews whether they had worn a mask during past interactions.³ This second study, in which the rate of infections was measured after the face mask use, is therefore not prospective but the type of study that is likely to suffer from recall bias. A meta-analysis of 33 randomised and observational studies, including studies done in schools and universities, showed no effect of face masks on the probability of developing influenza-like illness.⁴ Finally, in a Danish randomised controlled trial done (April–May, 2020), the recommendation to wear surgical masks outside the home (concomitant to other adopted public health measures) did not reduce SARS-CoV-2 infection rate in mask wearers at conventional levels of statistical significance.⁵ In June, 2020, WHO advised that governments encourage the public to wear masks under two conditions: when community transmission is apparent and when physical distancing is difficult, such as on public transport, in shops, or in other confined or crowded environments.⁶ When community transmission is widespread, we agree with recommending face masks in hospitals, in assisted living communities, and where at-risk populations are cared for. Conversely, existing data do not support universal, often improper, face mask use in the general population as a protective measure against COVID-19. Nevertheless, universal face mask policy (ie, in any indoor environment) is still adopted in certain countries. Public health mandates must be based on unequivocal and strong evidence and metered on the current local epidemiological condition.

We declare no competing interests.