Does this control for people actually getting measles? I.e., are the incidences of disease less after removing the people who got measles who didn't receive the MMR vaccine? Measles is known to strip the immune system of much of its memory, rendering people who have had it susceptible to all sorts of diseases they used to have protection against. I would not be surprised at all if this led to a large outcome differential for the vaccinated and unvaccinated, even if only a few of the unvaccinated caught measles.

I didn’t notice until your comment and it’s too late to edit now, but the first place I wrote “vaccine” should have been “virus”, see also my response to myself.

(Revaccinatiom may be needed after rituximab, which was specifically designed to attack immune memory cells in case if autoimmune disease - which apparently measles does as well - but the MMR vaccine doesn’t do that. I just typeda wrong word and didn’t notice)

Do you have a link to a paper or a study on that? Because the study I read I don't recall anything about the non vaccinated group having had measles, and that would be an obvious parameter to control for.