Mumps is a viral infection of the salivary glands, especially the parotid glands that run along the angle of the jaw in front of and below each ear. Children between the ages of 5 and 10 are most likely to contract mumps. Being infected once gives you lifelong immunity.
Mumps is most common around the month of March. It usually appears in scattered individual cases, though there are occasional local epidemics among unvaccinated children. It's less infectious than chickenpox or measles. Unvaccinated adults who never had the disease are at much higher risk of complications than are children, but mumps rarely causes serious problems.
A vaccine for mumps dramatically reduced the incidence of the disease since its introduction in 1967. In the 1950s, Canada had about 30,000 cases a year. The advent of the vaccine cut that number in half. Today, there are under 100 cases per year.