Another measles case has been reported in Kane County, the Kane County Health Department said Wednesday, this time in an individual who was vaccinated against the illness.
The second case of the year in the county, the health department says the person who was more recently confirmed to have measles was a contact of the county’s first case, which was reported late last month.
There have been almost a dozen measles cases in Illinois so far in 2026, a year that has already seen nationwide numbers exceed the total tally for the year prior.
The two cases in Kane County are its first since 2019, and two of only four cases reported in the county in the past roughly 30 years.
Measles is considered one of the most contagious viruses known to medicine. The disease can spread through the air when an infected person coughs or sneezes, according to the state’s Department of Public Health. Symptoms can include high fever, cough, runny nose, red eyes and a rash that often begins on the head and then spreads.
The individual reported to have measles last month in the county was an unvaccinated student at Kaneland High School in Maple Park. The possibility of others being exposed ultimately prompted the school to shift to a day of online learning less than two weeks into the new school year.
This new case in Kane County was a contact of the first case, which generated up to 1,600 potential exposures, per the health department. As part of its response to the initial measles case, the county health department identified two locations where individuals may have been exposed — Kaneland High School on Aug. 18 and Next Generation Pediatric Clinic in South Elgin on Aug. 21.
The individual more recently confirmed to have measles, whose identity has not been disclosed, was present at the high school last week while infectious, according to Michael Isaacson, the Kane County Health Department’s executive director, but is now out of isolation. Isaacson noted that individuals who were unvaccinated should have been in quarantine and not present at the school during that time.
Of its more than 1,100 students, about 97.7% of students at the high school are vaccinated against measles, according to figures from the Illinois Department of Public Health
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, a rate that slightly exceeds both the county and state averages for school children during the 2025-26 year.Vaccination rates nationwide, however, have fallen in recent years to below the 95% coverage needed to prevent outbreaks of the disease, and the United States’ measles-free status is slated to be reviewed later this year.
Although the case reported Wednesday was in an individual who was vaccinated, the health department is continuing to urge the measles, mumps and rubella, or MMR, vaccine as an effective means of preventing measles.
Two doses of the vaccine are about 97% effective, the county health department says, and the primary risk is to those who are unvaccinated.
Nevertheless, breakthrough infections — measles cases in vaccinated individuals — can occur, the health department said in a news release Wednesday. People who develop measles despite being vaccinated, however, generally have milder illness, are less likely to experience severe illness and may be less likely to spread the virus to others, according to the health department.
Individuals may be able to check their vaccination records on Vax Verify, or they can obtain records from their previous healthcare provider, school, employer or state immunization information system where the vaccinations were given. People who are unsure whether they’re protected against measles should contact their healthcare provider, according to the health department.
People born before 1957 are generally assumed to have immunity to the disease because of how widespread it used to be.
Individuals who are vaccinated but who may have been exposed to measles should monitor for symptoms for 21 days after their last potential exposure, per the news release from the health department.
Anyone who develops symptoms should stay home and call their healthcare provider before going to a medical facility so that they can provide instructions and prevent potential exposure to others, the health department said. Those who remain symptom-free through the end of the monitoring period do not need to take further action related to this exposure.
Individuals who are unvaccinated and who were potentially exposed to the first case in the county have been contacted directly by the health department and were already under quarantine, the news release Wednesday noted. These people should follow the quarantine instructions provided by the health department and should not attend school, work, social activities or other public gatherings during the quarantine period. They should also stay separated from family members as much as possible, per the health department.
The new case does not change the quarantine instructions for those already under quarantine unless contacted by the health department directly, the news release indicated.
The health department says it is currently reaching out to those who were contacts of the second case to provide quarantine guidance and will provide specific instructions based on exposure. As of Wednesday afternoon, the department said identification of contacts is ongoing, and not all contacts had been reached yet.
The health department is still identifying if there are potential exposure sites related to the new case, according to Isaacson.
Additionally, the Kane County Health Department also warned of an ongoing measles outbreak in southwestern Wisconsin. The state has seen 159 confirmed or probable cases this year as of Tuesday, with the vast majority concentrated in Grant, Iowa and Lafayette counties, according to figures from the Wisconsin Department of Health Services.
Given that the area is a popular destination for visitors from northern Illinois, particularly with the Labor Day holiday weekend having passed recently, the health department is encouraging residents who traveled there to be aware of the outbreak and to monitor for symptoms of measles, particularly if they are not vaccinated or are unsure of their vaccination status.
The Associated Press contributed.