It is time to talk about the unthinkable. What if immunity -- herd or otherwise -- is not possible? News from South Korean suggests reinfection may be a possibility so we cannot discount it and need to think about how our policies will play out if we are in SIS rather than SIR.

First of all, SIS means that we can't hope for immunity. Absent interventions, a share (R0 - 1)/R0, of the population will be infected at any given time. There is no waiting for vaccines or herd immunity. There is a priority on anti-virals for continual treatment.

Second, containment requires that we cannot just get R < 1 and hope for it to die out. We need to get to pretty much 0 infected. Nothing else will prevent it from re-emerging. The other option is to just live with it (may 1/3 sick all of the time).

Third, how can this be done? This means a long, long period of extreme social distancing OR we have continual testing, tracing and isolation OR a mixture of both.

What this means is that @paulmromer 's plan to put all of our eggs in the basket of testing whether people are currently infected or not, is the *only* policy that can *both* deal with SIR and SIS situations.