Fig. 8.

SEIIR epidemiology model. Sensitivity with respect to the symptomatic and asymptomatic fractions${\nu }_{\mathrm{s}}$and${\nu }_{\mathrm{a}}$. Darkest curves correspond to the special case of only symptomatic transmission, ${\nu }_{\mathrm{s}}=1.0$ (left) and only asymptomatic transmission, ${\nu }_{\mathrm{a}}=1.0$ (right); lightest curves vice versa. For the special case with similar symptomatic and asymptomatic infectious periods, $C_{\mathrm{a}}=C_{\mathrm{s}}$, the SEIIR model reduces to the classical SEIR model with $I_{\mathrm{s}}={\nu }_{\mathrm{s}}I$ and $I_{\mathrm{a}}={\nu }_{\mathrm{a}}I$. The set of blue curves illustrates the symptomatic part of the recovered population $R_{\mathrm{s}}={\nu }_{\mathrm{s}}R$; the steepest blue curve is the total recovered population $R$, which is independent of ${\nu }_{\mathrm{s}}$ and ${\nu }_{\mathrm{a}}$. Latent period $A=2.5$ days, symptomatic and asymptomatic infectious periods $C_{\mathrm{s}}=6.5$ days and $C_{\mathrm{a}}=6.5$ days, and contact rate $\beta \left(t\right)={\beta }_0-\frac{1}{2}[1+tanh([t-t^{\ast }]∕T)][{\beta }_0-{\beta }_{\mathrm{t}}]$ with ${\beta }_0=0.65$ /days, ${\beta }_{\mathrm{t}}=0.10$ /days, $t^{\ast }=18.61$ days, and $T=10.82$ days.