The modeling rule is that humans can be in one of three states: susceptible, infective or resistent. At the outset everyone is assumed susceptible and the first infectives have a field day, as per an MIT paper.
papers.ssrn.com/sol3/Papers.cf…
papers.ssrn.com/sol3/Papers.cf…
For this reason the disease spreads fastest at the beginning. Curves may vary but the steepest part of each curve is at the start when the ratio of susceptibles to infectives is high.
After a time people who survive the infection become noninfective and presumably resistant. The distribution change in susceptibles, infectives and resistants change and the rate of spread begins to slow down.
Thus each epidemic has a finite length on the x axis. It will "burn out". The task of control measures is to ensure the curve is shallow rather than high. This of course is an oversimlification ignoring new disease variants and reinfections from outside a community.
One of the limitations of a simple model is that it's bounded by the time horizon of the disease itself. It does not and probably cannot, consider the larger impact of the disease and the efforts to fight it.
The after effects of the Black Death to use an extreme example were profound. It was followed by invasions, famine, cultural trauma and revolutionary progress.
en.wikipedia.org/wiki/Consequen…
en.wikipedia.org/wiki/Consequen…
There is astonishingly little written about the effect of the Spanish Flu on the subsequent course of 20th century history. Yet it killed many more than the Great War over a far shorter period and the GW is widely blamed for killing Europe.
