Measles Outbreak Confirmed As Cases Rise In Illinois: IDPH

ILLINOIS — Two new measles cases have been confirmed in Illinois, making six in total for 2025, according to the Illinois Department of Public Health. The new cases were linked to Southern Illinois, adding to the two in the Marion area that were identified in April.

One of the new cases was confirmed over the weekend is in the Franklin-Williamson Bi-County area, which means the number now meets the technical Center for Disease Control and Prevention definition of an "outbreak" in that area (three or more cases that are linked to one another). Social links between the three cases are known.

"The risk to the general public from measles remains low," IDPH Director Dr. Sameer Vohra said. "The key to preventing measles is the highly effective MMR vaccine. Two doses are 97 percent effective in preventing this serious infection. I recommend that our Illinois residents make sure they and their family members are up-to-date on the MMR vaccine and all other age-appropriate immunizations."

IDPH said two unrelated cases were previously confirmed in Cook County. Another Southern Illinois case may have visited locations in Missouri, including the St. Louis Aquarium, according to health officials.

As Patch previously reported, one case in Cook County was identified as an adult who is a suburban Cook County resident, and whose vaccination status is unknown. They went to a local hospital for medical care on April 28, and were quickly isolated, according to the Cook County Health Department.

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Another case was identified in an adult Chicago resident who traveled internationally through O’Hare Airport in early April. The individual had one prior dose of the MMR vaccine. This patient had rash onset on April 25 and had been isolated at home since being diagnosed, according to the health department.

Current information on potential sites where infected individuals may have exposed others can be found on the IDPH website at Measles Exposure Locations.

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