Fig. 1.

Schematic of the epidemiological model. Compartments: susceptible to the virus ($S$); exposed ($E_1$); exposed, pre-symptomatic, and infectious ($E_2$); symptomatic and infectious ($I$); quarantined ($Q$); and recovered or deceased ($R$). Recovered individuals are assumed to be immune. The model includes analogous variables for individuals practicing physical distancing: $S_{\mathrm{d}}$, $E_{1\mathrm{d}}$, $E_{2\mathrm{d}}$, $I_{\mathrm{d}}$, $Q_{\mathrm{d}}$, and $R_{\mathrm{d}}$. Solid arrows represent flow of individuals between compartments at rates indicated by the mathematical terms. Dashed lines show which compartments contribute to new infections. An individual in some compartment $X$ can begin distancing and move to the corresponding compartment $X_{\mathrm{d}}$ at rate $u_{\mathrm{d}}$. The reverse transition occurs at rate $u_r$. The model quickly settles on a fraction $e=u_d∕(u_d+u_r)$ participating in distancing, and dynamics depend on this fraction, rather than on the rates $u_d$ and $u_r$.

Reproduced from Anderson et al. (2020b) for clarity.