Antivaccine beliefs occur at the same prevalence on the left and right, only the GOP promotes policies to make opting out of vaccines easier. All over the country, Republican politicians are opposing making school vaccine mandates stricter, proposing laws to loosen vaccination requirements, and falling for antivaccine pseudoscience.
Contrary to the stereotype of antivaccinationists as hippy-dippy left wing granola crunchers, in actuality antivaccine pseudoscience is the pseudoscience is the pseudoscience that knows no political boundaries. Unfortunately, that doesn't mean that both parties are equivalent. Unfortunately, thanks to the co-opting of conservative activism by antivaxers, the Republican Party in 2018 has become the antivaccine party.