The University of Missouri is urging student groups to halt some social events as the number of mumps cases continues to rise.

The Student Health Center said Wednesday that there are 128 confirmed and probable cases. The outbreak began in early November with four confirmed cases.

Most of them are linked to students in fraternities and sororities. Besides urging student groups to curtail events, steps to control the outbreak also include canceling a late night breakfast during exam week.

Mumps is a viral infection that causes swelling in the salivary glands and cheeks. All infected students received the required two doses of a vaccine that protects against mumps, as well as measles and rubella. But the vaccine doesn’t prevent all infections.

Anyone with symptoms is asked to stay at home.