Figure 4.

Assessment of the impact of face mask usage, as a sole intervention, on COVID-19 pandemic in the U.S. Simulations of the model (2.5)–(2.6), showing cumulative mortality, as a function of time, for (A) face mask transition parameters (α₁₂ and α₂₁) maintained at their baseline values, (B) mask-wearers strictly adhere to wearing masks (α₂₁ = 0) and non-mask-wearers transit to mask wearing at their baseline rate (α₁₂ ≠ 0), and (C) non-mask wearers and mask-wearers do not change their behavior (i.e., α₁₂ = α₂₁ = 0). Mask use change is implemented in terms of changes in the initial size of the population of individuals who wear face masks (from the onset of simulations, on October 12, 2020). Blue curves (in each of the plots) represent the baseline scenarios where the initial size of the population of mask wearers is fixed at 30%, and the transition parameters, α₁₂ and α₂₁, are maintained at their baseline values. Parameter values used in the simulations are as given by the baseline values in Tables 3, 4, with different values of α₁₂ and α₂₁ (except for the blue curves, where α₁₂ and α₂₁ are fixed at their baseline values).