Susceptible-Exposed-Infected-Removed

A method for modeling Epidemics.

Process

1. Susceptible ($S$) - No contact with the virus
2. Exposed ($E$) - Caught the disease, no signed of being able to infect others yet
3. Infectious ($I$) - Able to infect others
4. Recovered ($R$) - No trace of infectious disease left

Population

With $N$ as the total population, $N=S+E+I+R$

Other Formulas

• The rate of recovery is proportional to the number of infected and time $△R\sim \gamma I△t$
• The rate of infection is equal to those not currently infected and the number of exposed and time $△I\sim -\gamma I△t+\alpha E△T$
• The rate of exposed is proportional to $\beta :$ number of contacts per person per day, times those susceptible and the percentage of infected with time, minus those already exposed $△E\sim \beta S\frac{I}{N}△t-\alpha E△t$