Note that we are not evaluating the effect of universal mask-wearing for the public but that of mask-wearing for employees. The effect of universal mask-wearing for the public could be larger if people comply with such a policy measure. Tian et al. (2020) considered a model in which mask wearing reduces the reproduction number by a factor (1 - e \cdot pm)^2, where e is the efficacy of trapping viral particles inside the mask and pm is the percentage of mask-wearing population. Given an estimate of R_0 = 2.4Howard et al. (2020) argue that 50% mask usage and a 50% mask efficacy level would reduce the reproduction number from 2.4 to 1.35, an order of magnitude impact.