Just a little bit more on that.
Not only are the places with most infections mutating, but the more infections there are, the more opportunities there are for more unique mutations.
So the long-term focus really needs to be on reducing the size of (if not eliminating) the pool in which those mutations take place.
Smaller pool = less opportunities for mutations = less chance of the virus becoming more transmissible and/or more lethal ... or less amenable to being controlled/prevented/ameliorated by a vaccine.
It isn't enough to just vaccinate the US ... we have to vaccinate the entire world.
And the sooner the better.