Fig. 2.

Epidemiological impact of mask-wearing on COVID-19 transmission rate, measured by the effective reproduction number (R_t). (a) Illustration of R_t for two representative cases, R_t = 1 and R_t = 4, respectively. Adapted with permission from ref. [43]. Copyright 2020 JAMA. (b) R_t decreases with reported mask use. The plot is stratified by quartiles of the percentage of individuals who reported that they were “very likely” to wear a mask with family or friends and to the grocery store. Adapted with permission from ref. [45]. Copyright 2021 Lancet. (c) Effect of public mask wearing on R_t from an initial basic reproduction number R₀ = 2.4. The blue area is what is needed to slow the spread of COVID-19. Each black line represents a specific disease transmission level with R_t indicated. Adapted with permission from ref. [19]. Copyright 2021 PNAS. (d) Combined social distancing and mask wearing has the highest impact on reducing R_t. The horizontal dashed line was placed at R_t = 0.8 for community transmission control. Adapted with permission from ref. [45]. Copyright 2021 Lancet.