This specific scenario happens on my local Nextdoor groups all the time. I've answered responded with what I think is pretty clear and concise information, and then seem that same person ask the same question the very next day in a new thread. (And the next day, and the next...) I cannot help but conclude they're not really looking for an answer.
Maybe I'm a jerk, but I'd be inclined to answer the second question with "I answered that yesterday. Why do you keep asking if you aren't going to listen to the answers?" And reply with that every single time they re-asked the question.
But... Nextdoor... does that mean it's your physical neighbors? That might make me hesitate to do so. Or maybe I'd still do something like the same, but worded more gently and politely.
Here are some links to polls about American views on vaccines. It seems unlikely you’re running into this ratio without some major biasing factor.
https://www.washingtonpost.com/news/the-fix/wp/2015/02/09/he...
https://www.pewresearch.org/science/2021/03/05/growing-share...
(I’ll admit the numbers in September from the Pew poll are surprising to me)
Granted, you’re further assuming the person asks questions about vaccines. In your description it seems to me that we’re already far away from scientific thinking as a society if the way we can confirm someone is anti-science is by whether they exhibit symptoms of any kind of curiosity. This sounds like what the previous commenter is talking about.
Maybe you’re saying, “people who spread doubt in the form of a disingenuous question frequently do so in a particular social environment I’m a part of.”