Mumps increase in Flanders, Belgium, 2012-2013: Results from temporary mandatory notification and a cohort study among university students

Incomplete protection by two doses of mumps-containing vaccine, possible waning immunity and intense social contacts may have contributed to the occurrence of this outbreak in Flanders. Efforts to maintain high vaccination coverage with two doses remain essential. However, the reasons for low vaccine effectiveness must be further explored and additional immunological research for more immunogenic mumps vaccines is necessary.