I think the answer is: there is a limit to how transmissible Covid can get. I don’t know that there’s a way to prove that it can’t get worse than Delta, but when I look at nextstrain.org and consider that Covid has now has been hosted by billions of people, and has had several orders of magnitude more opportunities to replicate and evolve, and as of yet it hasn’t come up with anything much better than Delta.
I know I just said this above, but will give some more context. A few months ago I asked a similar question. https://www.lesswrong.com/posts/mXBBHAEXj2JyPC6Dt/is-there-a-theoretical-upper-limit-on-the-r0-of-covid
I think the answer is: there is a limit to how transmissible Covid can get. I don’t know that there’s a way to prove that it can’t get worse than Delta, but when I look at nextstrain.org and consider that Covid has now has been hosted by billions of people, and has had several orders of magnitude more opportunities to replicate and evolve, and as of yet it hasn’t come up with anything much better than Delta.