International Journal of Epidemiology 2002;31:978–982

The increased use of mumps vaccine worldwide has reduced the incidence of complications associated with mumps caused by wild virus, including aseptic meningitis, which occurs in up to 10 % of people with wild-virus mumps.1 However, as wild-virus mumps circulation has declined and mumps vaccine use has increased, adverse events associated with the mumps vaccine have come under increasing public and scientific scrutiny.2,3 Moreover, intensified efforts towards measles elimination and rubella control has led to recent expanded use of mumps vaccine in developing countries, particularly in the Americas: a key strategy for measles elimination is mass vaccination campaigns,4,5 with measles vaccine frequently administered as a combination vaccine including rubella and mumps vaccine strains. In May 2001, recommendations for mumps vaccine use were discussed by an expert committee at the World Health Organization (WHO),6 Geneva. Participants reviewed data on reactogenicity of mumps vaccine strains, as well as available information on immunogenicity, efficacy, cost, and supply. Mumps © International Epidemiological Association 2002 Printed in Great Britain The risk of aseptic meningitis associated with the Leningrad-Zagreb mumps vaccine strain following mass vaccination with measles-mumps-rubella vaccine