Back in the 70’s, right out of high school, I spent a summer working on the crib ward of the State Hospital which was turned into a prison in the mid 80’s).
About half the elderly patients there were brain damaged by measles in early childhood or rubella in utero before vaccines where developed. Almost none of the “clients” in this mental institution had actual mental illness. They were mostly brain damaged by accident or illness with very low functioning, many blind or deaf or both.
We were slowly moving them to nursing homes, preferably near a relative if one could be located and was interested.
People have been killed, and other horribly damaged by these diseases.
In very small numbers.
Minuscule in relative terms.