I think you’re correct that the difference between R0 and Rt is that Rt takes into account the proportion of the population already immune.However, R0 is still dependent on its environment. A completely naive (uninfected) population of hermits living in caves hundreds of miles distant from one another has an R0 of 0 for nearly anything. A completely naive population of immunocompromised packed-warehouse rave attendees would probably have an R0 of 100+ for measles.I don’t know if there is another Rte type variable that tries to define the infectiveness of a disease given both the prevalence of immunity and the environment. Seems like most folks just kinda assume that environment other than immune proportion is constant when comparing R0/Rt figures.
Dan, both you and Elizabeth make good points here that I hadn’t given enough consideration to (I wish I could tag both of you in a comment somehow, but I’m not sure if that’s possible).
Yes, it is dependent on the population/community but also there’s several different ways to calculate it making it hard to compare not just between diseases but also between R0 calculations for given diseases… So… yeah that makes a straight-forward objective ranking of contagiousness a much more difficult task I suspected from the table in the article… it also makes talking about contagiousness objectively somewhat more difficult than I hoped.