Calling anti-vaccination people “anti-science” is a transparently bad persuasion tactic. Leave a social line of retreat.
Also, it probably isn’t even true that they’re anti-science. It’s more likely their stances on science are inconsistent, trusting it to varying degrees in different situations depending on the political and social implications of declaring belief.
I think speaking in terms of probabilities also clears up a lot of epistemological confusion. “Magical” thinkers tend to believe that a lack of absolute certainty is more or less equivalent to total uncertainty (I know I did). At the same time, they’ll understand that a 50% chance is not a 99% chance even though neither of them is 100% certain. It might also be helpful to point out all the things they are intuitively very certain of (that the sun will rise, that the floor will not cave in, that the carrot they put in their mouth will taste like carrots always do) but don’t have absolute certainty of. I think it’s important to make clear that you agree with them that we don’t have absolute certainty of anything and instead shift the focus toward whether absolute certainty is really necessary in order to make decisions or claim that we “know” things.