Mumps outbreak among young people in Northern Ireland.

An outbreak of mumps occurred in the Mid-Ulster area of Northern Ireland between 1st November 1999 and 31st August 2000, with 729 cases notified. Salivary test results were obtained for 430 (59%) reported cases, of which 332 (77%) were positive for mumps IgM antibody. Three hundred and sixteen (95.2%) of these confirmed cases were in the age range 9 to 19. One hundred and eighty-four (55.4%) confirmed cases had received one dose of MMR (measles, mumps and rubella) vaccine, but only 3 (0.9%) confirmed cases had received 2 doses of MMR. The low incidence of mumps among children who had received two doses of MMR illustrates the importance of the second dose of MMR for full protection.