Fig. 2.

SEIR epidemiology model. The SEIR model contains four compartments for the susceptible, exposed, infectious, and recovered populations. The transition rates between the compartments, $\beta$, $\alpha$, and $\gamma$ are inverses of the contact period $B=1∕\beta$, the latent period $A=1∕\alpha$, and the infectious period $C=1∕\gamma$. If the transition rates are similar for the symptomatic and asymptomatic groups, the SEIIR model simplifies to the SEIR model with $I_{\mathrm{s}}={\nu }_{\mathrm{s}}I$ and $I_{\mathrm{a}}={\nu }_{\mathrm{a}}I$.