We have the genetic capabilities to trace back the initial arrivals in the US and other countries. Some of the reports I have seen say most of the US invasion came in through NY from Europe. Also seen reports and suggestions that a somewhat less virulent form was here in the US as early as November. Unfortunately, at that time we weren't looking.

When I worked with fish diseases the pathologists regularly tried to remind folks that we can't say "It's not here" because we haven't looked for it. Same with Covid, the world started looking when people started to die.