I think I can say with reasonable confidence that I was wrong in my prior estimations of a super-low herd immunity threshold. Things are not looking good for COVID in most of the world. Colorado is seeing 10 times as many daily new cases as in the summer, and the United States as a whole is looking almost as bad. Colorado was barely untouched, so that doesn’t say much about the herd immunity claims, but then there’s Europe.

Europe looks so much worse than it did in the Spring. The UK, Spain, France and even Italy. The daily new case rate is hard to compare since we maxed out on testing capacity in March, pretty much all over the world. But the deaths do not lie, and they’re ramping up on a curve that looks like it’s going to match Spring. These are hard-hit places I’d expect to see showing some signs of immunity in this wave, but it’s not showing up anywhere I can see it.

But… why? The common claim is behavior has been returning back to normal. That’s maybe true, but what about Sweden? As far as I can tell Sweden has been fairly consistent in their response and they are seeing an enormous uptick in cases that I think we’d be hard-pressed to explain away with behavior changes.

Weather is starting to seem a likely culprit. I think it better explains the rise in the autumn than behavior shifts–the behavior shifts started in early summer and if that were the driving force, I’d have expected the uptick in cases to start way earlier than it did.

Where do we go from here? As long as we’re able to stay under capacity in hospitals, I think that full-scale lockdowns like we saw in the Spring continue to be unwarranted, and probably impossible anyway. But for those of us who can stay at home, now is the time to do it. It’s probably more important now than it was when everyone did it, and furthermore there’s an end in sight. In March, it was ridiculous to suggest that the majority of the world stay at home until there’s a vaccine, but given that we’re close now, this seems a more reasonable request now.

Stay safe and stay at home if you can.