Face masks for the public during the covid-19 crisis

TLDR

The authors argue that, amid a rapidly spreading, untreated COVID‑19 pandemic with rising deaths and strained health systems, the limited and contested evidence on mask efficacy warrants applying the precautionary principle and prioritizing external validity over internal validity. The study contends that policymakers should adopt the precautionary principle and promote mask use, emphasizing external validity in mask evaluations. The authors conducted a rapid literature search that identified five peer‑reviewed systematic reviews on public mask use during epidemics.

Abstract

Trisha Greenhalgh and colleagues argue that it is time to apply the precautionary principle The precautionary principle is, according to Wikipedia, "a strategy for approaching issues of potential harm when extensive scientific knowledge on the matter is lacking." The evidence base on the efficacy and acceptability of the different types of face mask in preventing respiratory infections during epidemics is sparse and contested.12 But covid-19 is a serious illness that currently has no known treatment or vaccine and is spreading in an immune naive population. Deaths are rising steeply, and health systems are under strain. This raises an ethical question: should policy makers apply the precautionary principle now and encourage people to wear face masks on the grounds that we have little to lose and potentially something to gain from this measure?3 We believe they should. Evidence based medicine tends to focus predominantly on internal validity—whether primary research studies were "done right"—using tools to assess risk of bias and adequacy of statistical analysis. External validity relates to a different question: whether findings of primary studies done in a different population with a different disease or risk state are relevant to the current policy question. We argue that there should be a greater focus on external validity in evaluation of masks. A rapid search of the literature on the wearing of masks by the general public during epidemics or pandemics by a team at the University of Galway (E Toomey, personal communication, 29 March 2020) found five peer reviewed systematic reviews: