I would have to suspect fraud as the simplest cause, but perhaps also people demanded multiple redundant vaccines.
Is there info on flu vaccine vs COVID for elderly in California?
Non fraud explanations I could come up with:
Medical tourism? I vaguely remember reading stories of foreign nationals coming to the US to jump the queue for vaccination in their own country or to get mRNA vaccine unavailable in their home country. New Hampshire, Maine, the Dakotas might have had Canadians coming as tourists or for the vaccine or other medical treatment that required vaccination.
"A relative in Paraguay told radio there the family was visiting Miami for COVID-19 vaccinations."