[zaroth]

Every increase in the percentage of people with immunity reduces R0. At some point, even absent any other measures, the R0 would be below 1 just due to the number of people that are immune; herd immunity.

But in any case, the immunity level of the population reduces the need for other measures in order to stay below an R0 of 1.

There’s a massive spectrum of efficacy in the dozens of different suppression or containment policies that can be applied, combined with demographics and geography of the location being studied.

But in any case, the immunity level of the population is a downward force on R0 that, for example, will naturally keep daily cases lower in New York vs. Florida regardless of policy.