Health officials have issued an urgent warning after a measles exposure at Chicago O’Hare International Airport, where an infected adult spent April 22–23 in Terminal 1 between 10 a.m. and 8 p.m. “Measles can linger in the air for hours,” raising concerns that hundreds of travelers may have been exposed. The person, who had received one MMR dose, developed a rash on April 25 and is now isolating.

A second case was later confirmed in the same Illinois county. The individual, whose vaccination status is unknown, sought hospital treatment on April 28 and was quickly isolated. Health officials are tracing contacts, warning that measles can cause serious complications in unvaccinated people, especially children and those with weak immune systems.

Authorities urge anyone who was in O’Hare’s Terminal 1 during those days to watch for symptoms like fever, cough, runny nose, red eyes, and rash. “Call your healthcare provider before visiting” if you suspect exposure, they advise.

Officials emphasize that two MMR doses offer strong protection. The CDC and Chicago’s health department are working to contain the outbreak, noting that rising travel and gaps in vaccination threaten herd immunity against this once-eliminated disease.