I am not sure what you are referring to as 'three stage'. Herd immunity appears on a graph as a classic bell curve; look at a graph of Sweden's infection rate - who took no precautionary action - for March to June. By June the incidence is statistically nil. States here that opened up in June are about three months behind Sweden.
We see this every year with the seasonal flu. Vaccinations may influence the overall numbers but not the shape of the bell curve. Eventually everyone will be exposed to the coronavirus; as long as there is not massive lockdowns that is inevitable. By fear govt autocrats can impose indefinite lockdowns thus destroying the U.S. economy and seducing the population in to socialism.
Not complicated.
This is what bugs me, it seems like the Prez is helpless to stop this scenario. I don't get it.
Notice the change from COVID-19 to just coronavirus?
Coronavirus can cause the common cold.