Thirteen percent of the confirmed measles cases in the U.S. this year have resulted in hospitalization, according to the CDC, including 21% of cases in children five or younger. Three people are confirmed to have died. At the same time, experts stress that this issue goes beyond measles.

Measles cases in the United States have reached their highest number in more than 30 years, according to new federal data published Wednesday.

While measles symptoms typically resolve in a few weeks, the virus can cause pneumonia, making it difficult for patients, especially children, to get oxygen into their lungs. It may also lead to brain swelling, which can cause lasting damage, including blindness, deafness and intellectual disabilities.