Chicago reports first measles case of 2025 linked to O'Hare Airport travel

In the United States, measles cases are on the rise, prompting health officials to take action in Chicago, Illinois. The city recorded its first confirmed measles case of the year involving an adult resident who traveled internationally through O'Hare Airport in early April 2025. This individual had received one prior dose of the MMR vaccine, which was followed by the onset of a rash on April 25. The patient was diagnosed and has since been isolated at home. Public health officials are particularly concerned since breakthrough infections, although rare, can occur among vaccinated individuals when their immune response is insufficient. As of April 30, 2025, two confirmed cases of measles have been identified in Cook County, with the first noted in a southern Illinois adult on April 23. The second case involved a suburban Cook County adult with an unknown vaccination status who sought medical care on April 28. Chicago and Cook County health authorities are urging residents to ensure they are fully vaccinated to prevent further transmission of the disease. They have also released warnings for individuals who may have been exposed in various locations, including O'Hare Airport, and other establishments during specific dates in April. The Illinois Department of Public Health has pointed out the high contagion rate of measles—90% of susceptible individuals close to an infected person will also become infected. To combat the outbreak, health officials emphasize the importance of receiving two doses of the MMR vaccine at least two weeks prior to any international travel. They have been proactively notifying anyone who might have been exposed to the infected individuals. In spite of the MMR vaccine's history of safety and effectiveness over the past 50 years, misinformation surrounding vaccinations has contributed to a decline in immunization rates, exacerbating the current measles outbreak in the country. Health professionals are encouraging unvaccinated individuals or those with incomplete vaccination histories to consult their healthcare providers to ensure they are adequately protected against the virus.