Map shows measles cases across U.S.

Measles cases popping up across the United States, including an outbreak in Texas that has led to the death of a child, are prompting questions about where exactly the illness has been detected.

Measles is one of the most contagious infectious diseases, and in some cases can cause severe infections in the lungs and brain that can lead to cognitive issues, deafness or death. But doctors and health officials say the vaccine, which is normally given as part of the combination measles-mumps-rubella (MMR) vaccine, is highly safe and effective.

While most people's symptoms improve, about 1 in 5 unvaccinated people who get measles will be hospitalized. About 1 out of every 1,000 children with measles will develop brain swelling that can lead to brain damage, and up to 3 of every 1,000 children who become infected will die, the CDC says.