A vaccinated DuPage County resident has tested positive for measles after recently returning from international travel, marking the county's first confirmed case of the year. The resident passed through Terminal 5 at Chicago O'Hare International Airport on Oct. 15, and anyone who was there between 4:20 p.m. and 7 p.m. that day may have been exposed.
Health officials described the infection as a rare breakthrough case, since the resident had already been vaccinated, according to NBC Chicago. Breakthrough infections in vaccinated people are uncommon but possible, particularly after intense or prolonged exposure to someone carrying the virus, the station reported. People who passed through that terminal during the exposure window were urged to report it to their local health department, per guidance cited by CBS News Chicago.
DuPage health officials assessed the risk to the general public as low, even as they urged vigilance among anyone who may have crossed paths with the traveler. Those who were exposed are being told to monitor for symptoms over a 21-day window, which can include fever, cough, runny nose, red and watery eyes, and a rash, as reported by FOX 32 Chicago. The rash typically appears three to five days after the other symptoms begin, usually starting on the face before spreading downward, per CBS News Chicago's reporting.
What the Rash Can Look Like
On lighter skin, the measles rash can appear as pink, red or reddish-brown flat spots and raised bumps, while on darker skin it may show up as darker, dusky or purplish-brown areas that can be more subtle and feel bumpy or textured, according to CBS News Chicago. Anyone with questions about a rash that might be related to measles should call their doctor right away, the outlet reported. People who do develop symptoms are asked to stay home and call ahead before showing up at a doctor's office or emergency room, explaining the possible exposure so the facility can take precautions, per FOX 32 Chicago.
Illinois' Department of Public Health notes that anyone unsure of their own vaccination history should notify their health care provider, who can determine whether testing is warranted if symptoms appear. DuPage residents who believe they were exposed are asked to call the county health department at (630) 682-7400, according to NCTV17.
Vaccinated Doesn't Mean Immune, but It Helps
Vaccinated people who do contract measles typically experience milder illness, are less likely to suffer complications, and may be less likely to spread the virus to others, the station's report noted. Vaccination lowers the risk of infection and transmission in the first place, and when a breakthrough case does occur, it tends to result in milder symptoms, per the same account.
The MMR vaccine covers measles, mumps and rubella, and provides lifelong protection against measles and rubella specifically, though its effectiveness against mumps can wane over time, CBS News Chicago reported. People who have received two doses of the MMR vaccine are considered protected against measles, and anyone born before 1957 is also considered protected, the outlet noted.
A Statewide Picture of Rising Cases
This isn't the first time O'Hare's Terminal 5 has triggered a measles exposure alert this year. In April, Cook County officials warned that a contagious individual had passed through the same terminal in late March, with possible exposure for anyone there between 10:45 a.m. and 2:30 p.m. on March 24, according to the Chicago Tribune. That same person also visited two suburban stores in Niles and an immediate care center in Mount Prospect before being identified, the Tribune reported, noting that measles can linger in the air for up to two hours after an infected person leaves a space and can spread after just 15 minutes of exposure.
Statewide, the Illinois Department of Public Health has confirmed 24 measles cases in 2026, with the DuPage County case standing as the only one confirmed in Illinois over the past week, per CBS News Chicago's report. The bulk of the state's cases are linked to an outbreak centered in Douglas County, located south of Champaign and east of Decatur, which has recorded 11 confirmed cases. Moultrie County has logged five cases, Madison County three, Kane County two, and Cook, DeKalb and DuPage counties one apiece, according to the same report. An earlier state update had placed the statewide total at 23 cases, attributing most of them to the Douglas and Moultrie counties outbreak, though the more recent count brought the tally to 24, with 79% of this year's cases occurring in people who were unvaccinated or whose vaccination status was unknown, NBC Chicago reported.
