I have some thoughts, due to the bit of divergence that's happening with cases.
Here in CO, people are a little antsy because there is a definite upwards slope on our cases and hospitalizations trendlines. But we are also doing well for vaccine distribution. We're also hearing similar from WA, OR, and then there was MI. Meanwhile, other places are starting to stall on vaccinations but cases are stable.
The answer is natural immunity. The states with higher natural immunity + their vax rate, is good enough, at this moment, to be outperforming the states with lower natural immunity + their vax rate. CO has the 10th lowest cases/100K, WA is 5th lowest, OR is 3rd lowest and MI now is 16th lowest (I'm guessing they were lower before this recent surge). This could indicate a couple of things.
First, we're almost there. Somewhere between the the places that are seeing rising trends and those that aren't, is an inflection point. If we continue to vax, we will get more states above that point, and approach the next one. However, the divergence is a reminder that if you don't take path A - vaccination, you will do it via path B - natural infection. Our map for where cases are climbing includes a lot of the counties with low vax rates. I am sure they thought with the snowflakes in Boulder getting their shots and feeling safer, that they could go back to normal and that would be that. Instead, the virus virused, and people getting shots in Boulder does nothing to protect your rural, under-vaccinated county and unvaccinated self if the virus is present. There are a couple states that have high cases/100K that are also showing some 7-day case rise, Arizona, Kansas. I suspect this is the divergence in the areas within the state that are either above the inflection point or below it. If there are areas of unvaccinated/not-immune people the virus continues to find it.
Second, natural immunity is providing adequate protection against the B.1.1.7 variant. Which would be good for both length of immunity and against variants. We know people can get re-infected, in general, but what percentage? Do the new variants make it worse? It doesn't seem like, for this one. There is a new study observing US Marines which resulted in a 10% re-infection. Probably a manageable number, that can be lowered even more with vaccination. If against the variant, there were lots of reinfections, the numbers would be rising everywhere. The divergence seems to indicate the infections are largely "newly infected people" and not reinfections. The P1 in Brazil still should be watched, because with what happened there seems like re-infection had to be a bigger problem. So we should continue to be mindful that just because natural immunity is protective now, doesn't mean it stays that way. But it's buying us time to vaccinate.