ZIONSVILLE, Ind. -- Students who are not vaccinated against chicken pox or previously had the illness will not be permitted to attend school at Zionsville Community High School beginning Monday because of an outbreak at the school, the Indiana State Department of Health said Friday.

Thirteen cases have been reported at the school. Health officials said an examination of records found that a few hundred students at the Boone County school may not have been vaccinated.

"Students who have not received two doses of the varicella (chicken pox) vaccine can only return to school once they can show documentation they have received the required varicella immunizations, or once we are certain the outbreak is over," said State Health Commissioner Dr. Gregory Larkin in a news release.

The Boone County Health Department will offer in-school immunization on Monday for chicken pox and other vaccinations required for school.

Students who aren't vaccinated for whatever reason, including medical issues or religious objection, will be forced to stay home until 21 days after the last chicken pox case is diagnosed, Larkin said.

“This action is based on school outbreak control guidance from the Centers for Disease Control and Prevention,” Larkin said. “Students who have not had chicken pox and are not fully immunized are vulnerable to catching and spreading chicken pox and must be excluded to protect them and others.”

Larkin said the requirement isn't punitive but is "an unfortunate reminder of why these vaccines are required."

Zionsville Superintendent Scott Robinson said he is glad immediate action is being taken.

"We've been giving notice about the second vaccination for many months," he said. "This is just a case of getting people to comply with that law."

Parents and students that 6News talked with said they weren't worried.

"My kids have both been vaccinated the recommended number of times, so I haven't been too concerned about it," said Gigi Nicholas.

"The principal just talked to us about it and he said he's not concerned about it at all," said student Will Stanczykiewicz. "The situation is all under control, so we should be OK."

So far this year, 222 cases of chicken pox have been reported in Indiana, health officials said.

Chicken pox is very contagious and is normally spread between children. Symptoms are normally mild, but can cause serious complications, including pneumonia, bacterial infections, encephalitis or even death.

Chicken pox is normally spread through coughing, sneezing or contact with a rash from an infected person.

People who have chicken pox are contagious from two days before the rash appears until it has scabbed.

More: School Immunization Requirements