Even for those 3%, the actual infection they get if they are exposed to measles post-vaccination is often a lot less problematic.
I was one of those kids where the vaccination did not take fully, and I got sick from my brother, who could not be vaccinated due to ongoing and chronic pulminary tract infections as a kid, and brought it home from kindergarten: some unvaccinated child with stable genius parents. He almost died from it too, while I just had the usual rash with a slight itch and super explosive diarrhea. Needs diapers at the age of six because getting to the toilet in time is impossible sort of explosive.
Fun fact, measles has a potential side effect in the form of Dawson disease, which is basically a time bomb planted by the measles infection that will go off in your brain, killing you without recourse. Fun disease, don't forget to bring your unvaccinated kids to a measles party.
The dumbest thing of it all is though that the distrust of the measles vaccination goes back to faked paper by Andrew Wakefield who wanted to discredit existing measles vaccinations to sell his own. The same sort of idiots who still cling to his disproven lies are the same ones that tell everyone that big pharma is just trying to make us sick for profit, popping sugar placebos with a 10000% price markup in the form of homeopathy.
If it weren't for the harm done to kids who are not to blame for their dumb parents, I'd be happy to see RFK stopping vaccinations entirely. The world's way too full of people anyway, and if some of the worst offenders of wasting resources want to off themselves in a terribly painful way, who am I to argue. Just go and die. Alas.