“In the US, 20 percent of people with measles are typically hospitalized. Five percent develop pneumonia, and up to 3 in 1,000 die of the infection. In rare cases, measles can cause a fatal disease of the central nervous system called Subacute sclerosing panencephalitis, which develops years after infection. Measles also wipes out immune responses to other infections (a phenomenon known as immune amnesia), making people vulnerable to other infectious diseases.”

https://arstechnica.com/health/2025/02/texas-measles-outbreak-climbs-to-48-cases-almost-all-kids-13-hospitalized/

We think of measles as a minor viral infection of kids that causes fever, rash, and a runny nose, and goes away without major complications. Unfortunately, that is not always so. Nervous system disease is a particular problem. SSPE occurs as a late, fatal measles complication in one out of 1,367 cases of measles in children younger than 5. One out of 1,000 children with measles gets an infection of the brain (encephalitis) early in the course of measles. About 15% of children with measles encephalitis die. Measles encephalitis led to the death of the writer Roald Dahl’s daughter Olivia.

Children’s brains can also develop an allergic reaction to the measles virus several weeks after infection. This is called acute disseminated encephalomyelitis (ADEM). Children seem to recover, then get fever, confusion, headaches, and neck stiffness. Like SSPE and measles encephalitis, ADEM occurs in about one out of 1,000 cases of measles. It is fatal in 10% to 20% of patients. Survivors of measles encephalitis and ADEM often have epilepsy, brain damage, or developmental delay.

Measles has other serious complications. During pregnancy, it causes miscarriages. Measles can infect the cornea, and was once a common cause of blindness. Ear infections and hearing loss are frequent. Measles virus also infects the lungs, causing pneumonia in 3% to 4% of cases. Measles weakens the immune system for at least two months. Sometimes patients die of other infections immediately after they recover from measles. In a measles epidemic that killed more than 3,000 soldiers in the US Army in 1917–18, bacterial pneumonia was the major cause of death.

Measles: The forgotten killer - John Ross, MD, FIDSA, Contributor; Editorial Advisory Board Member, Harvard Health Publishing