CHICAGO - A new report in a Centers for Disease Control and Prevention (CDC) journal highlights the rapid response of the Chicago Department of Public Health (CDPH), with support from the CDC and other partners, for curtailing a measles outbreak in a Chicago new arrivals shelter. The analysis conducted by CDPH and the CDC was published Thursday in the CDC's  Morbidity and Mortality Weekly Report (MMWR) and estimates the recent outbreak would have likely been significantly worse if not for the rapid, coordinated response.

Starting on March 8, CDPH, supported by the CDC, Cook County Health and other community healthcare partners, implemented a rapid public health response to a confirmed case of measles in a shelter. The response included a mass vaccination campaign, in which more than 9,300 doses of measles, mumps, rubella (MMR) vaccine were administered in new arrivals shelters. Additionally, more than 17,000 MMR doses were administered to other Chicagoans during the outbreak period. The response also included screening of shelter residents for measles symptoms, and isolation of people with suspected or confirmed measles. These interventions reduced the spread of measles and successfully reduced the outbreak size and duration, according to the report.

The last confirmed measles case associated with the shelter developed a rash on April 5, and the last case in Chicago developed a rash on April 16. CDPH will continue to monitor for related cases until May 30 when two full incubation periods (the time from when someone is exposed to measles until they develop symptoms) have passed since the last case. Although the outbreak in Chicago may soon be over, measles cases are on the rise domestically and internationally, and the threat of additional cases remains.

“This is a good example of what can be accomplished when federal, state, county and city agencies come together with community partners in a rapid and coordinated fashion to address an active outbreak,” said Stephanie Black, MD, MSc, Medical Director with the Disease Control Bureau at CDPH. “Offering MMR vaccination to eligible new arrivals and community members is the best protection against measles outbreaks. When measles cases do occur, rapid response is critical to prevent additional measles cases.”

The CDC developed mathematical models that showed the actions taken by CDPH and partners substantially reduced the likelihood of a larger measles outbreak in Chicago. Without rapidly implementing a mass vaccination campaign and actively screening people for measles symptoms, the CDC model predicted a high likelihood that more than 100 people would have become infected with measles during the outbreak. Instead, actions taken by CDPH and partners contained the outbreak, and at the time of publication 57 measles cases associated with the shelter outbreak had been identified.

For more information, visit the CDC's publication of the full MMWR, entitled Measles Outbreak Associated with a Migrant Shelter - Chicago, Illinois, February-May 2024 and the companion MMWR, entitled Real-Time Use of a Dynamic Model To Measure the Impact of Public Health Interventions on Measles Outbreak Size and Duration — Chicago, Illinois, 2024.

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