A cubic function? facepalm I'm not an epidemiologist, but I use statistics and mathematics in my work in academia and what he did was beyond stupid. A logistic function would have been a far better model, but he wouldn't have liked the results, I'm sure. Logistic growth models are used to model all kinds of biological phenomena such as population growth, and can also be used to model infections.

However, typically stochastic or compartmental models are used, the former being more realistic, the latter being easier to analyze. Those are probably beyond Excel, though. You would do that in something like the R programming language, or even Python.