CHICAGO (CBS) — The first week of school at the University of Illinois at Urbana-Champaign included a crash course in vaccinations, as health officials struggle to contain a growing mumps outbreak.

“The university sent out a message that they wanted all the students to get vaccinated before they came back to school. We know that not all of them did that, for whatever reason. So hopefully we’re going to get as many vaccinated as possible in these next few days,” said Champaign Urbana Public Health District Administrator Julie Pryde.

So far, about 100 confirmed cases of mumps have been reported on the downstate campus, but Pryde said that number is expected to grow.

“It all depends on how many people get vaccinated. Certainly we’re positioned for an explosive growth of this,” she said.

With the fall term getting underway this week, the district has set up an immunization clinic for the university’s 50,000 students and staffers. In the first half hour alone, they vaccinated 500 people.

“The state isn’t paying the bills, and we’ve got cutbacks in all the little health departments around us, and yet we put out the call,” Pryde said. “We have health departments that may have two or three nurses are sending staff here to help us.”

The Chicago Department of Public Health has confirmed a case of mumps, reportedly involving a student at St. Ignatius College Prep. It’s unclear if that case is in any way related to the outbreak at UIUC.

Pryde said anyone who has never had the mumps needs to get the full set of shots to protect against the viral illness.