Measles vaccination gaps raise outbreak risk in northern Illinois schools

State health officials are sounding the alarm across Illinois schools, where many districts fall below the vaccination threshold needed to prevent the spread of measles in local schools.

New data from the Illinois State Board of Education shows several counties in the region – including McHenry, DuPage, Kane, Grundy, Kankakee and Bureau counties – remain vulnerable because of uneven local coverage, a concern that’s only grown as measles cases climb nationally.

The Illinois Department of Public Health on Wednesday reported its first confirmed case of measles in 2025, involving an adult in southern Illinois, confirmed through laboratory testing April 23. Currently, this is an isolated incident; IDPH considers it not to constitute an outbreak.

As of mid-April, the Centers for Disease Control and Prevention has reported 800 confirmed measles cases across 25 jurisdictions, putting the U.S. on pace to surpass recent records before the end of the year.

To put that in perspective, the highest number of U.S. measles cases since the disease was declared eliminated in 2000 was 1,274 cases in 2019 – a total reached over the course of the entire year.

“You can have a county with over 95% coverage overall, but if one school or one district has lower rates, that’s all it takes for measles to take hold.”

—  Jennifer Seo, IDPH pediatric medicine medical adviser

Earlier this year, a measles outbreak in west Texas drew national attention after multiple children were hospitalized and public health officials worked to contain the spread in under-vaccinated communities. Two children died, including an unvaccinated child.

“What we’re seeing nationally is that measles doesn’t really stay contained,” IDPH pediatric medicine medical adviser Dr. Jennifer Seo said. “A single case can lead to a broader outbreak, especially in under-vaccinated communities. It reinforces why localized coverage is so important – even one vulnerable pocket can put a whole region at risk.”

The updated data reveals a decrease in Illinois’ measles vaccination rate, from 95.2% in the 2023-24 school year to 95.1% in 2024-25.

Although this drop is relatively minor, it continues a downward trend at the wrong time as outbreaks continue to spread across the country.

This slight dip marks the fifth consecutive year of declining measles vaccination rates among schoolchildren across the state, according to newly released IDPH data.

“There’s been a steady decline in our measles vaccination rates among school-aged children going back to the 2017-2018 school year,” Seo said. “While this year’s change was small, the broader trend is something we’re watching very carefully.”

What’s the impact of lower vaccination rates?

Public health officials recommend a minimum of 96% measles vaccination coverage in schools to maintain herd immunity – a level that helps protect those who cannot be vaccinated, including children with weakened immune systems.

“If a school is under 91%, they’re below the level that would confer herd immunity,” Seo said. “That simply means it’s going to be harder to stop measles from spreading from one student to the next.”

Despite Illinois maintaining an overall measles vaccination rate above 95%, several counties in the northern part of the state remain in a more vulnerable position.

According to data from the Illinois School Vaccination Coverage Dashboard, 10 counties in the region fall into the “yellow” tier, meaning their average school measles vaccination rates range between 91% and 96%.

These counties include Kane, Lake, McHenry, Bureau, Winnebago, Ogle, DuPage, Grundy, Kankakee and Cook (Chicago).

Kathy Marshall, regional superintendent for Bureau, Henry and Stark counties, said local districts are aware of their vaccination data and continue to work closely with local health departments when needed.

“School districts here received IDPH information regarding measles data, although districts are already aware of their own local data due to reporting requirements,” Marshall said. “If school districts are concerned, they can work with their local health department to set up local clinics or provide families with further information regarding immunizations.”

Marshall said that although some students are exempt from immunizations because of religious reasons, school staff play a key role in ensuring families are informed.

“Our school district staff already does a great job of providing requirement information to parents as students go through school,” Marshall said.

As national measles cases rise, Marshall acknowledged that potential outbreaks are a concern – particularly during times of heavy travel.

“There are and have been cases in nearby states,” she said. “It is a very busy travel season for many families, so being exposed to any health-related illness is always a possibility.”

Bureau County is one of the three to fall into the “yellow” tier, with a measles vaccination rate of 95.5% – just below the 96% threshold needed to maintain herd immunity.

Although not alarmingly low, public health officials warn that rates below this benchmark leave schools more vulnerable to outbreaks.

“Even regions with decent coverage can be susceptible if there are pockets of lower rates, and that’s exactly what we’re seeing in many of our counties,” Seo said.

That effect was made clear during last year’s measles outbreak in northeast Illinois – ​the state’s largest in over three decades.

Sparked at a Chicago shelter for newly arrived migrants, the virus quickly spread into neighboring suburban counties, including Cook, DuPage, Lake and Will.

The outbreak led to 67 confirmed cases before it was contained in June.

Seo said the outbreak served as a wake-up call to school districts and public health officials in Illinois.

“Any time we see cases in our own backyard, it becomes very real for families and communities,” Seo said. “That outbreak highlighted just how quickly measles can spread in environments where even small gaps in vaccination coverage exist.

“You can have a county with over 95% coverage overall, but if one school or one district has lower rates, that’s all it takes for measles to take hold.”

Seo said the reasons for the decline in measles vaccination coverage vary by district and community.

Notably, traditional public schools continue to post higher vaccination rates across all immunization categories, compared with charter and private schools, according to IDPH and Illinois State Board of Education data.

Although the exact reasons behind this trend are not fully understood yet, Seo suggests it may stem from a combination of factors.

“It’s hard to say exactly why public schools have higher coverage, but it may simply come down to better access, stronger enforcement, and more alignment with public health efforts,” she said.

Seo also emphasized the importance of local-level solutions.

“To really improve coverage across the board, we have to take a more granular approach – looking school by school, community by community – to really understand what the specific barriers are and how we can address them."

IDPH targets districts below 96%

This approach prompted IDPH to begin reaching out earlier this month to schools with vaccination rates below 96%, offering resources, information on vaccine access and a survey designed to assess each school’s preparedness for a potential outbreak.

“As a pediatrician, I know how important vaccinations are for protecting children from preventable illnesses,” IDPH Director Dr. Sameer Vohra said. “As measles outbreaks spread through various parts of the United States, it is now more important than ever to make sure you and your family members are up to date with all age-appropriate immunizations.”

To explore the data or check vaccination coverage in your community, visit the Illinois School Vaccination Coverage Dashboard or Measles Outbreak Simulator Dashboard and navigate to the “School Vaccination Coverage” section.