Health officials in Illinois are investigating a cluster of measles at a Cook County daycare center, the Chicago Sun-Times reported.

Five children under the age of one, all with ties to KinderCare Learning Center, are being tested. Two of them have been confirmed to have measles, while results for the remaining three are still pending.

The Illinois Department of Public Health and Cook County Department of Public Health said in a statement that the source of the infection for the children is not immediately known.

According to the statement, all students, staff and faculty have been notified and anyone who has not had the measles, mumps and rubella (MMR) vaccine has been instructed to stay away from unvaccinated children for the next 21 days.

The Chicago Sun-Times was unable to reach a spokesperson for KinderCare.

Last week, a suburban Cook County resident was reported to be the first confirmed case of measles in the state, this year. That resident may have exposed other people at three locations in the area:  Northwest Community Hospital in Arlington Heights; Supermercado Guzman in Palatine and Vista Clinic, also in Palatine.

The measles outbreak has affected at least 102 people, nationwide, after originating in California’s Disneyland in December 2014. According to the CDC, children should be given their first dose of MMR vaccine at 12 to 15 months of age. The second dose should be given four weeks later, usually before the start of kindergarten.

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