My bet would be more likely these nuts who don’t vaccinate their kids. WHO interactive maps indicate that it is pretty much all but eradicated in most places except a few spots in the US- East and West coast and North/Central US.
That was a nice resource. Thank you for the link
Don’t know about the California epidemic, but Polio *was* all but erased and islam let it back in. On purpose. Claiming that vaccination was an “infidel” trick.