What's it got to do with SIR and predicting a 2nd wave? Is it a solution looking for a problem.One can look at it in different ways from the perspective of mathematics, but I think the answer for you is that in a classic diffusion model you can go in either direction with an equal probability. In a percolation model you can access somesiteswith a certain probability. Vide anomalous diffusion.

@"I feel the above is a case ofargumentum ad verecundiam."

It probably means that you need to educate yourself a bit on the subject(s) if you want to discuss them ;-

Waiting for your next jibe ..