There were 2 studies in 2019 that involved about 100 people total between the both of them that tested the prevalence of certain antibody peptides using a new (introduced 2015) device called VirScan. If we look at the conflict of interest statement we see that people who were involved in the study hold the patent on the VirScan device, so they're not going to question it's accuracy. Also members of the GlaxoSmithKline Vaccine Research and Development Advisory Board, so they're not going to question their product. And it is a product, and the best kind too, the mandatory kind. Here's the gist of the study:
77 unvaccinated children mean age 9 (+-2 years) were studied using this new machine before and 2 months after recovering from measles. The machine has a library of the proteins of 400 viruses. Children with severe cases had a median decrease of 40% of antibody epitopes that the machine could detect, and children with mild cases had a median decrease of 33%. All children recovered their antibodies after natural re-infection.
So the whole thing rests on: 1. the accuracy and reliability of the machine, and 2. a temporary effect that sounds spooky scary but is ultimately meaningless because all the test subjects were over 5 years of age, so they've essentially already survived until adulthood (except for suicide and accidents).
A reversible effect that has no impact on mortality measured after all of 2 months to me is meaningless.