There are certainly plenty of people who have rather strange beliefs. There are a lot of ways to slice the vaccination data. The CDC estimates that 87.6% of adults in the U.S. have gotten at least one dose. The hard core antivaxxers are a fringe group.
Flat earthers are even more fringy:
"firm belief in a flat Earth was rare, with less than a 2 percent acceptance rate in all age groups."
A poll says lots of Millennials evidently do—and it’s not entirely clear why
blogs.scientificamerican.com
I wouldn't say it's literally overtaken the country.