Urgency and uncertainty: covid-19, face masks, and evidence informed policy

As the covid-19 crisis deepens, Greenhalgh and colleagues say that policy makers should encourage the public to wear face masks.1 Given the urgency of the situation, they argue that any downsides to such a move would be heavily outweighed by the benefits. We think that the potential negative unintended consequences of a policy shift deserve more consideration.

First, the technical challenges in mass mask adoption should not be underestimated. Even healthcare workers can struggle with appropriate mask use2; cloth masks are less effective than medical masks3; and poor use reduces effectiveness and poses an infection risk.4 Second, encouraging uptake of face masks might lead to “risk compensation”: reduced compliance with other measures.56 Third, there are potential societal consequences, such as a rush to obtain equipment intended for use by healthcare workers should cloth masks prove ineffective or using mask wearing to justify unsafe workplaces or commuting conditions.7 Finally, the indirect consequences of an intervention in a complex system are inherently difficult to predict. Both anticipating unintended consequences8—such as potential to increase anxiety rather than offer reassurance9—and adaptation of measures after implementation10 are vital. Policy, however, is a blunt tool; premature change in policy impedes both.

The global challenges wrought by the pandemic are unprecedented, and demand has engaged academia. But public communication about the scientific view of the risks and benefits of widespread uptake of face masks has exceeded the evidence. A lay summary of the evidence for face masks authored by Greenhalgh and Howard declares simply that “the science says yes” to masks.11 Alongside Greenhalgh’s analysis piece,1 the principal source for this claim is an unreviewed literature review with very limited methods, susceptible to bias.12 Such unequivocal advocacy for face masks risks overstepping current knowledge and promoting policy change based more on eminence than evidence.