I suspect the number of American kids who haven’t gotten the MMR vaccine is less than 1%.
Heck, I'm "middle-aged", and recently received boosters to this and to my DPT, given all that is being allowed to come across our borders unchecked, and that I have a new infant granddaughter that I do not want exposed.
I have not, however, has a flu shot, nor do I intend to do so.