The US federal government can require it by passing laws if they see fit to do so. Presumably the states with the highest Covid infection rates would fight it i

The US federal government can require it by passing laws if they see fit to do so. Presumably the states with the highest Covid infection rates would fight it in court on some constitutional basis to avoid vaccination, and some armed citizens would kill medical personnel enforcing the federal directive, but none of that prohibits the laws from being passed.