Perhaps the most terrifying is a condition called subacute sclerosing panencephalitis, or SSPE, in which the virus lies dormant in the brain of someone who recovered from a measles infection and reawakens 7-10 years later to cause “a progressive dementia that is almost always fatal,” Kasson wrote.
This outcome is rare, but it does happen. The Los Angeles County public health department reported a case in September 2025.
