Thin sectioned transmission electron microscope (TEM) image depicted the ultrastructural details of the mumps virions that had been grown in a Vero cell culture. A member of the genus Rubulavirus, the mumps virus is the pathogen responsible for causing mumps in human beings, with an average incubation period of 16 to 18 days, and ranging between 12 to 25 days. Mumps can be prevented with MMR (measles-mumps-rubella) vaccine. MMR vaccine prevents most, but not all, cases of mumps and complications caused by the disease. Two doses of the vaccine are 88% (range: 66-95%) effective at preventing mumps; one dose is 78% (range: 49%-92%) effective.