Health officials are issuing an urgent warning after a possible measles exposure at Chicago O’Hare International Airport. An infected adult, contagious at the time, spent two full days in Terminal 1.

The individual had received one prior dose of the MMR vaccine but still contracted the illness. They were present at the airport on April 22 and April 23 between 10 a.m. and 8 p.m., raising concerns that hundreds of travelers may have been exposed.

Measles is one of the most contagious viruses known. It can linger in the air for up to two hours after an infected person leaves the area, meaning anyone passing through Terminal 1 during those times may be at risk.

By April 25, the traveler developed the signature measles rash and has since been isolating at home. Officials emphasize that early isolation is key to preventing additional spread.

Days later, a second measles case was confirmed in an adult from the same Illinois county. The person’s vaccination status has not yet been disclosed, but they sought care at a local hospital on April 28.

Medical staff acted quickly, isolating the patient upon arrival to minimize risk to others. Still, health authorities are carefully tracing contacts connected to both cases.

Measles can cause serious complications, particularly for young children, pregnant women, and those with weakened immune systems. Pneumonia, brain swelling, and even death are possible outcomes in severe cases.

Officials urge anyone who may have been at O’Hare during the exposure times to check their vaccination records. Those who are unvaccinated or unsure of their immunity should contact a healthcare provider immediately.