During the most recent measles outbreak in the US: 1 in 4 victims were hospitalized. 1 in 20 will develop pneumonia. 1 in 1,000 will develop swelling in the brain causing brain damage and death. Victims remain susceptible to brain complications up to eight years after infection, even if the initial disease was mild.
"In 1962, children's book author Roald Dahl lost his oldest daughter, Olivia, to measles. She was 7 years old."
http://www.npr.org/sections/goatsandsoda/2015/02/03/383305152/beyond-rash-and-fever-how-measles-can-kill