By Alexandra Sifferlin
Updated: February 5, 2015 9:50 PM ET

Five infants attending a KinderCare Learning Center in Chicago have measles.

According to NBC Chicago, two of the infants were confirmed with lab tests and three were confirmed based on symptoms, but have lab tests that are still pending. All of the infants are under the age of 1.

The first dose of the vaccine for measles, MMR, is supposed to be given to children starting at 12 through 15 months and a second dose at 4 through 6 years. Given the age of the infants, it is possible they were not vaccinated yet.

“We began the contact investigation to learn about the different places where exposures could have occurred, learn more about the symptoms, and see if there are any other unvaccinated individuals in the home,” says Amy Poore-Terrell, director of public relations at the Cook County Department of Public Health.

Staff and students of the center were told to stay home and away from unvaccinated people for 21 days if they had not received a measles vaccination. Poore-Terrell says individuals at the facility who are unvaccinated are at a risk, and nurses with the department are already in contact with them.

The last exposure at the facility was on Feb. 3 and Poore-Terrell says the health department informed the day care to exclude anyone who was unvaccinated from returning the next day. Since the virus circulates in the air for up to two hours, she says they do not have reason to believe the virus was circulating when other unvaccinated people where at the center. It has not undergone special cleaning.

A case of measles had been reported in Chicago a month ago. NBC reports that only 10 cases of measles had been reported in the state of Illinois over the past five years.

The new cases add to more than 100 cases reported in 14 states in the U.S. this year. The Centers for Disease Control and Prevention will likely release updated numbers on Monday.

Contact us at editors@time.com.

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