Figure 4.

Epidemiological risk metrics as a function of the probability, $m$, that an infection is mild (as a result of mask-induced variolation). In each panel, results are shown for three situations, corresponding to the original SARS-CoV-2 wild-type, and the Alpha, Delta and Omicron variants (for which ${\mathcal{R}}_0=3,4.5,6.75\hspace{0.17em}\mathrm{and}\hspace{0.17em}28.4$, respectively; cf. table 2). (a) Basic reproduction number (equation (4.1)); the estimated values of ${\mathcal{R}}_0$ for each variant are assumed to be associated with ineffective variolation ($m=0$). All other parameters are set to the default values indicated in table 3 (the Canadian birth rate is assumed). (b) Doubling time T₂ (equation (4.11)); for the original wild-type (WT), the curve extends far above the vertical maximum of the plotted graph (T₂ → 65 days as $m\to 1$). (c) Peak prevalence of severe cases (§4.6). (d) Expected final proportion of the population that will have experienced a severe illness (equation (4.19)). (e) Equilibrium prevalence of severe cases (equation (4.5c)).