The United States continues to battle increasing cases of the measles, a highly contagious disease that can cause serious, occasionally life-threatening, complications. The measles virus spreads through respiratory droplets, usually from somebody coughing or sneezing, and the infectious particles can remain active in the air for up to two hours.

How contagious is it? “Let’s say I have the measles and I was in a room of 10 people who didn’t have the vaccine,” says Gail F. Shust, MD, pediatric infectious disease specialist at Hassenfeld Children’s Hospital at NYU Langone. “Nine out of those 10 people would get the measles.”

A fever, cough, runny nose, or red eyes typically present first before the rash appears. If your child has a fever and red, painful eyes, contact a pediatrician and ophthalmologist right away. The number one thing parents can do to prevent measles is to get their children vaccinated.

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