The SEIR model is a slightly more advanced compartmental epidemiology model. Here, we add an additional component to represent exposed individuals. Exposed individuals become infectious after an incubation period, which is the time starting from when a person is first exposed to a virus and ending when symptoms first emerge.

With the added factor of an incubation period, you will notice the simulation disease curve is spread out over a larger period of time. For many diseases, this is more realistic as it will take time for the virus or other contagion to spread throughout the body.