Health officials are urgently warning the public about a potential measles exposure at Chicago O’Hare International Airport after an infected adult spent two days in Terminal 1. The individual, who had received one prior dose of the MMR vaccine, was contagious while at the airport on April 22 and 23 between 10 a.m. and 8 p.m. each day. Measles, one of the world’s most contagious diseases, can linger in the air for hours, raising concerns that hundreds of travelers may have been exposed. The infected person later developed a rash on April 25 and has since been isolating at home.

A second measles case was identified days later in an adult from the same Illinois county, though their vaccination status remains unknown. This individual sought treatment at a local hospital on April 28, where medical staff quickly isolated them to prevent further spread. Health officials are now working to trace potential contacts from both cases, as measles can lead to severe complications, especially in unvaccinated individuals, including young children and those with weakened immune systems.

Authorities are urging anyone who was at O’Hare’s Terminal 1 during the exposure window—or who may have had contact with either infected person—to monitor for symptoms such as high fever, cough, runny nose, red eyes, and a distinctive rash. Those who suspect exposure should contact their healthcare provider immediately but call ahead to avoid spreading the virus in waiting rooms. Measles is highly preventable with two doses of the MMR vaccine, which health experts emphasize is safe and highly effective.

This incident marks the latest in a series of measles exposures at major U.S. airports and communities, highlighting gaps in vaccination coverage. Chicago’s health department is coordinating with the CDC to contain the outbreak, while urging vaccination for those who are unimmunized. As travel continues to rebound, officials stress the importance of herd immunity to prevent future outbreaks of this once-eliminated disease.