Huh.

«…little-known complication of measles known as immune amnesia. This is a phenomenon in which portions of the immune system’s memory are wiped clean. It occurs because the measles virus can invade not only the cells of the respiratory system, but also the cells of the immune system. This includes the memory B cells, which are specialized white blood cells whose job is to recognize pathogens that the body has encountered and fought off before. When alerted by the memory B cells that they have come across a known pathogen, the immune system can swiftly mobilize the specific antibodies it needs to target and overcome the invader.

Without that early warning system in place, the immune system is perpetually flying blind. This leaves the person susceptible to contracting secondary infections from other pathogens, including those that they have successfully fought off before. Researchers have found that, after recovering from the measles, the immune system is suppressed for at least several months, and for up to two years.»

https://www.uclahealth.org/news/article/measles-infection-can-cause-immune-amnesia