I have been trying to learn more about the SIR model since hearing about it due to recent events. In the process, I have heard various contradictory things. So I am seeking clarity. Specifically, I want to make sure I understand the R in SIR correctly. Does R stand for removed (ie, recovered or dead) or recovered?
It is my understanding that S is for susceptible (percentage of living population not yet infected) and I is for infected (percentage of contagious population).
Because the simplest SIR model implicitly assumes a recovered individual cannot transmit the virus (ie, immunity), I am inclined to think R has to be for removed to ensure that S+I+R=1; since the simplest SIR model does not account for population changes due to variable birth/death rates, I'm not sure that this equality relation holds. It follows that dS/dt + dI/dt + dR/dt = 0 ==> dR/dt = - (dS/dt + dI/dt), which makes me wonder: what is the model actually capturing regarding R?
