Fig. 2.

The SEIQR model with delays. Healthy individuals $S\left(t\right)$ are infected with rate constant $\beta$. Infected individuals $E\left(t\right)$ remain asymptomatic and non-infectious for a time duration $\sigma$. Subsequently, these individuals become infectious and enter population $I\left(t\right)$, but remain asymptomatic for a time duration $\tau$. Upon showing symptoms, they enter population $Q\left(t\right)$ and are quarantined with probability $p$ for a time $\kappa$, beyond which they infect nobody. Some infectious asymptomatic individuals may become non-infectious on their own, with rate $\gamma$. After quarantine, the cured population $R\left(t\right)$ could in principle lose immunity at a small rate $\alpha$, but we take $\alpha =0$ for a fast-spreading pandemic.