SEIR Model

The SEIR model is a compartmental mathematical model in epidemiology that divides a population into four groups, those Susceptible to infection, those Exposed who have been infected but are not yet themselves infectious, those currently Infectious, and those who have Recovered and gained immunity, tracking the movement of individuals between these compartments over time with a system of ordinary differential equations. It extends the earlier SIR model, introduced in 1927 by the Scottish biochemist William Ogilvy Kermack and the Scottish military physician Anderson Gray McKendrick, by adding the Exposed compartment to explicitly capture a disease's incubation period, the interval during which an infected person carries the pathogen but cannot yet transmit it to others. This extra compartment makes the SEIR model far better suited than the simpler SIR model to diseases with a substantial latent period, such as measles or chickenpox, where ignoring the delay between infection and infectiousness would otherwise distort predictions of how quickly an outbreak spreads. Like the SIR model, the SEIR model yields a basic reproduction number that determines whether an outbreak will grow or die out, and numerous further compartments, such as ones for vaccination or asymptomatic carriers, are commonly added to it for specific diseases.