Five babies at a suburban Chicago day care center have been diagnosed with measles, The Chicago Tribune reported Thursday, citing local health officials.

Childhood vaccination has become an emotionally charged topic in recent months amid a measles outbreak that has sickened more than 100 people across the United States and in Mexico. No deaths have been reported.

The outbreak has drawn increasing attention to a growing anti-vaccination movement, with some parents opting not to immunize their children, citing religious beliefs or the fear that vaccines may be linked to developmental problems such as autism. While every U.S. state requires children to provide proof of immunization before entering public school, most states offer parents religious exemptions from vaccinating their kids before enrollment, and 18 states allow them to skip vaccinations because of personal beliefs, according to the Johns Hopkins Institute for Vaccine Safety.

In the Chicago area this week, health officials are investigating the cluster of measles cases at KinderCare Learning Center in suburban Palatine, the Tribune report said. All the children are under a year old.

Two of the cases were confirmed with laboratory testing while the other three diagnoses had test results pending, the paper said.

It said the center’s administration has notified students and staff at the center to remain at home if they have not received the measles, mumps and rubella (MMR) vaccine.

MMR vaccinations are not recommended for children as young as those diagnosed with measles at the day care center, according to the U.S. Centers for Disease Control and Prevention (CDC). The CDC advises that children get their first dose of the vaccine at 12 to 15 months, followed by a second at 4 to 6 years.

Al Jazeera and Reuters