However, during outbreaks, vaccine effectiveness for two doses ranged CSF-1R inhibitor from 61% to 91% [6]. In 2002, the WHO European Region

introduced a strategic plan to eliminate measles and prevent congenital rubella infection by 2010. The plan involved increasing vaccine coverage with the measles, mumps, rubella (MMR) vaccine to at least 95%. Hence, a parallel aim was to reduce annual reported rates for mumps to under 1/100,000 by country [4]. From 2006 to 2010, in Europe, mumps rates decreased from 8.7 to 1.98/100,000 [7]. However, at the same time, several countries reported large outbreaks [8], [9], [10], [11], [12] and [13]. From 2004 to 2005 on, one of the first large mumps outbreaks in a vaccinated population occurred in England and Wales [8], including 2,562 laboratory confirmed cases in 2012 [14]. From 2009, the Netherlands reported a mumps outbreak that started among students and evolved into a large national outbreak with 1662 cases until June 2013 [15]. These outbreaks and other outbreaks, such as those in the United States, shared common features [9]. First, young adults were most commonly affected. Second, cases clustered among students with intensive

social contacts (e.g., classes, shared living facilities). Third, affected young adults were often vaccinated with two-doses of mumps vaccine. In 1984, the general Flemish vaccination scheme included MMR vaccination with a first dose administered at the age of 10–12 months. In 1995, a second dose Isotretinoin administered at the age of 10–12 years was added. The vaccination strain used Protein Tyrosine Kinase inhibitor in Flanders is Jeryl Lynn (MMRVax®, Priorix®) [16]. The vaccination coverage for children aged 18–24 months (first dose of MMR) and children aged 14 years (second dose of MMR) is estimated in Flanders using two-stage cluster sampling surveys, that take place every

4–5 years. The most recent coverage assessment was performed in 2012 [17]. In Belgium, incidence of mumps prior to general vaccination was estimated at 500/100,000 in 1985 and declined to 49/100,000 in 1994 [16]. Mumps is not a notifiable disease in Belgium. However, in Flanders, the regional public health office requires medical doctors and authorities of educational institutions to notify clusters of several diseases, including mumps. Between 1995 and 2010, smaller clusters of mumps cases and one outbreak in 1995/96 in partly vaccinated children aged 8–12 years were reported [6]. In the spring of 2011, regional public health authorities of Antwerp (a province of Flanders) reported a mumps outbreak with 164 cases, mostly among young adults [18]. In 2012, medical doctors from Ghent reported a new cluster of mumps among students of the University [19]. This outbreak spread to campuses and universities in other provinces.