The University of Missouri wants students to get their booster mumps shot. The University of Missouri is urging students to obtain a booster mumps shot to protect against an outbreak that has grown to 193 confirmed and probable cases. The school says all the students sickened since the beginning of the fall semester had received the required two doses of a vaccine that protects against mumps, as well as measles and rubella. University health officials said Wednesday that a third shot may offer more protection. The school says most of the sickened students have recovered, with at least 169 of them well enough to return to class without risking infecting others. Mumps is a viral infection that causes swelling in the salivary glands and cheeks. The university is among several across the nation that has grappled with outbreaks this year.