Anti-vacc transcends political affiliation.
RFK was very much a lefty darling for years (decades?) with ridiculous support amongst "Hollywood".
And, as anyone who remembers The Pandemic can attest, one of the biggest talking points when the COVID vaccines were rolling out was that anyone who insisted everyone get vaccinated was actually super racist because America experimented on Black People a couple decades ago.
Its the same with "alternative medicine". Chuds insist we should inject bleach into our gooches because of 5G radios. Granola eating lefties insist we should use holistic medicine based on East Asian secrets because they are cultured and it is better for the environment (while the Tiger Moms are calling everyone dumbasses and saying to just get vaccinated because science).
The reality is that it all basically boils down to the vilification of intellectuals. And much of that goes back to long standing efforts by conservative/government orgs. The republicans have been focusing on it, especially in media, since reagan but it goes way back towards burning philosophers and proto-scientists at the stake.
One really funny side effect of this is that the better part of a decade ago, trump actually said something like "I like vaccines" at one of his rallies and his ass got booed REAL abrahamic god damned hard. Which is why he is constantly on the "We are putting too many vaccines into the babies" bullshit because it lets him feel like he is speaking his truth while not getting turned on by his mob.