A conservative assessment applied to the COVID-19 estimated R0 of 2.4 (7) might posit 50% mask usage and a 50% mask efficacy level, reducing R0 to 1.35, an order of magnitude impact rendering spread comparable to the reproduction number of seasonal influenza. To put this in perspective, 100 cases at the start of a month becomes 31,280 cases by the month’s end (R0 = 2.4) vs. only 584 cases (R0 = 1.35). Such a slowdown in case-load protects healthcare capacity and renders a local epidemic amenable to contact tracing interventions that can eliminate the spread entirely.

A full range of efficacy e and adherence pm is shown with the resulting R0 in Figure 1, illustrating regimes in which growth is halted entirely (R0 < 1) as well as pessimistic regimes (e.g. due to poor implementation or population compliance) that nonetheless result in a beneficial effect in suppressing the exponential growth of the pandemic.

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