Also, as Josh Marshall points out, the segment of the population with the greatest voter participation (age 65+) is also the segment of the population with the highest rate of vaccination (over 90%). So among likely voters, opinion is even more skewed against the anti-vaxxers.
On top of that, outside their little subculture, anti-vaxxers are really unpopular in the wider- mostlyvaccinated society . I see that attitude in my own life. Anti-vaxxers are blamed for the Delta variant, the new mask requirements, etc., even though the variant arose in India completely independently from the American anti-vaxxers. Knowing that hasn't stopped me from getting pissed off at them. Even if they are not responsible for the Delta variant, their actions make the next dangerous Greek letter more likely.
With most Americans, especially the demographics most likely to vote, increasingly hostile to the anti-vax cause, it seems really dumb for Republicans to hitch themselves to that particular wagon as we head into the midterm campaign season. And sure, the midterms are more than a year away. A lot can happen before them. The COVID situation could be completely different (I sure hope it is). But tarring their own brand with anti-vax lunacy is not a good way to start the Republican campaign to retake Congress.