I still believed in vaccines before Covid. Everybody has been raised on the success of the vaccines for smallpox, rabies, polio, measles, etc., which used to kill millions. I know there are arguments against these points now, but when I was young, older adults remembered seeing people die from these things, and viewed vaccines as a modern miracle. That mindset held until just before Covid, for most people.
Even now, I lean towards RFK Jr's perspective on it. At first there were a handful of vaccines that were well tested, and seemed to have a clear benefit. The smallpox vaccine is an obvious example. Smallpox is said to have killed more people than all the wars in history, and the vaccine reliably prevented it. However, now the big pharma companies have something like 70 vaccines that children are supposed to get, which were developed under a corrupt testing regime, to address diseases with marginal risks. The current vaccine regime is highly questionable whatever people might have thought about vaccines 70 years ago. Of course the kicker is that the Covid "vaccine" is not even a real vaccine.
Trump would have been solidly in the vaccine believers category for all his life before 2020. Even Elon Musk probably was. By now, a lot of people, including me, have seen how crooked the Covid situation was, and now we don't trust the other vaccines either. It takes time for this doubt to spread. The battle against vaccines won't truly be won until honest studies have shown the fraudulent nature of the vaccines and pharma companies, and they have been sued into bankruptcy. That battle will probably take 10-20 more years, with big pharma fighting back the whole way.
At least Trump has come around to support RFK Jr., and is supposedly going to put him in a position where he can really fight this fight.