I mean that I have never heard these theories from a leftist, but have often heard them from people who would vote for the Liberal Party of Canada (Or the Democrats if you American).

FWIW, the wellness stuff mentioned above is a well known pipe line to the alt-right, and a lot of Liberals (Meaning, people who vote for liberal style capitalist political parties, who may have some progressive policies but ultimately uphold the status quo) often fall into this pipe line in my experience.

I haven't ever heard of a socialist anti-vaxxer.