John wrote up the [SIR model](https://www.azimuthproject.org/azimuth/show/Blog+-+stochastic+epidemic-type-1D-models) in the Azimuth library and his blog on network theory. This has Recovered and Resistant in the Petri net but it would be interesting to add the SEIR model to the page which adds Exposure to the SIR model as in a Covid-19 SEIR paper I read the other day which I'll post a link to when I can find it.