Also called Subacute sclerosing panencephalitis (SSPE), it affects like 1 in 5,000 people who contract measles (vaccinated), but jumps to 1 in 609 in the unvaccinated.
Basically, you get measles and then seem fine, but anywhere from months to 15+ years later, you develop brain inflammation, seizures, spasms, blindness, and coma, and it’s basically 100% fatal. The disease attacks your nerves and brain. There’s no treatment or cure, and it hurts the whole time you’re dying. It can take months or more of excruciating suffering to kill you. It’s similar to rabies, in that you lose all control and are guaranteed a protracted, painful death.
It’s preventable by getting the measles vaccine.