Infectious diseases such as influenza or Covid-19 are often modelled using so called ‘compartment models’, that split the population into different groups depending on infection status and potentially other forms of demographic or geographical factors.
Two of the simplest models are SIR and SEIR. The difference is that the former has a three stage model of disease progression: susceptible–infected–recovered; whereas the SEIR model adds an extra category `exposed’ for those who have caught a disease, but are not yet infectious.
The following will use discrete time versions of each, with daily changes, but there are also continuous time models.
- SIR model – Susceptible Infected, Recovered
- SEIR model – Susceptible Exposed Infectious, Recovered