Table 1.

Description of model parameters.

Parameters	Biological meaning
$\Lambda$	Recruitment rate
$\mu$	Natural mortality rate
$\sigma$	Infectious factors for $A$
$\omega$	Disease-induced death rate
$\alpha$	Modification parameter for $S_1$
$\beta$	Effective contact rate for infected
${\gamma }_1$	Recovery rate of asymptomatic individual
${\gamma }_2$	Recovery rate of infectious individual
$\delta$	Progression rate from exposed become infectious
$\pi$	Proportion of recruitment to be high-risk susceptible
$p$	Proportion of exposed individuals that become asymptomatic