Perhaps superior medical resources is a factor here. Mutations seem particularly likely to arise in individual patients who don’t die, but carry infection for a long period. It may be that we’re better are treating people so we have a relatively smaller proportion of people with chronic infections, and/or we’re better at isolating them so mutations that arise don’t spread.
I also don’t know that the US has been doing the same genetic tracking other places have. So we don’t even know what’s come from here.
True. No doubt there has been texas and florida variants.
Consider the population density of a country like, say, India versus the U.S. Keep in mind, the virus literally evolves within an infected person, and it can keep changing within that person’s body as long as some of those billions of copies of the virus are still alive and kicking within the infected individual. Not to mention, it can spread to tens if not hundreds of individuals as that person sheds virus.