I know Anti-vaxxers. I know many personally, and they are also all over the internet. Some of my best friends were in the community, and so is my aunt.
They are all super online and very passionate about this debate and talk about it, read about it, and research it all the time. They all have their anti-vax communities. MAGA roped that crowd in as part of the conspiracy theory groups they roped in as well.
This movement is not a mainstream media movement, its formed in private facebook groups, forums, telegram chats, discord, and other places. They all know RFKj because he also is a part of the movement, and has been long before he was part of this administration.
Politics have changed Ned. Anti Vax rhetoric (which, horseshoe theory also had a lot of crunchy leftists in it a decade ago) and that community wasn't always political. Covid changed that, only because it fit their narrative (vaccines are under researched, bad, and less effective than they are helpful), and thus it became more mainstream and a function of the MAGA political movement.