This started off as a notebook about ecological metapopulations, the basic model of which is identical to the SIS model of disease. In fact, what I posted was half of the actual notebook: the main one starts with a section on metapopulations (I have deleted that for students who are just interested in disease models). And that metapopulation notebook is one chapter in what is effectively a textbook (about 12 notebooks) on computational ecology! It was for a graduate course with that title. What I posted here is a spin-off that I use in a different undergraduate course. Sadly, I haven't taught the computational ecology course for a while. The notebooks are not in terrible shape, but the code would need some polishing if I taught it again. Especially as that course was intended also to introduce students to coding in the Wolfram Language. But I'd like to!