Vaccine 22 (2004) 2713–2716 Outbreak of mumps in a vaccinated child population: a question of vaccine failure? Corinne Vandermeulen a,∗ , Mathieu Roelants a , Marijke Vermoere b , Katelijn Roseeuw b , Patrick Goubau c , Karel Hoppenbrouwers a a Department of Youth Health Care, Katholieke Universiteit Leuven, Kapucijnenvoer 35/1, 3000 Leuven, Belgium b Pupil Guidance Centre Brugge(n), Sint-Maartensbilk 2, 8000 Brugge, Belgium c Laboratoire de Réference Sida, Université catholique de Louvain, Avenue Hippocrate 54/92, 1200 Bruxelles, Belgium Received 27 March 2003; received in revised form 24 December 2003; accepted 3 February 2004 Available online 21 February 2004 Abstract In Belgium, children are immunized against measles–mumps–rubella (MMR) in a two-dose schedule at the age of 15 months and 11 years. Despite these recommendations, epidemics of mumps still occur. During an outbreak of mumps in Bruges (Belgium), 105 cases were registered in seven schools (age group 3–12 years). Lower than optimal vaccination coverage, inadequate vaccination schedule and a combination of primary and/or secondary vaccine failure are considered as possible reasons for the outbreak as described in the article. The role of secondary vaccine failure is highlighted. © 2004 Elsevier Ltd. All rights reserved. Keywords: Outbreak; Mumps; Vaccination 1. Introduction Prior to vaccination, mumps was an infectious disease that occurred frequently among primary schoolchildren (5–9 years of age). In Belgium, the first mumps vaccine, licensed in 1967, was recommended for general use at the age of 15 months (boys only) in 1980. Since 1985, a first dose of trivalent measles–mumps–rubella-(MMR)-vaccine was rec- ommended for all 15-month-old toddlers (boys and girls), followed by a second dose at the age of 11 years (fifth grade in primary school) since 1995. From the onset of the MMR-vaccination program Pluserix ® (Urabe strain; Glax- oSmithkline) was used in Belgium, which was systemati- cally replaced by MMR Vax II ® (Jeryl Lyn strain; Aventis Pasteur MSD) in the year 1993 (withdrawal of Pluserix ® from the market). In the years following general vaccina- tion a sharp decline of reported mumps cases was noted in Belgium (Personal communication of Van Casteren, Scien- tific Institute of Public Health, Belgium) and in several other countries [1–3].During the last decade, several outbreaks of mumps have occurred in Belgian schoolchildren. Before the introduction of a second dose of MMR in the US in 1989, ∗ Corresponding author. Tel.: +32-16-33-68-73; fax: +32-16-33-68-83. E-mail address: corinne.vandermeulen@med.kuleuven.ac.be (C. Vandermeulen). county or state-wide outbreaks of mumps occurred mainly among junior high school students, despite high vaccination coverage (95–98%) [1–3]. Primary and secondary vaccine failure have been put forward as possible explanations for the outbreaks, but evidence for waning vaccine-induced im- munity was found in only two of the three outbreaks that looked for secondary vaccine failure [1,2]. In this study, we describe a mumps outbreak in several kindergarten and primary schools in the region of Bruges (Belgium) and try to define underlying causes. 2. Materials and methods The study population consists of all pupils from seven kindergarten and primary schools in Bruges, having re- ported at least one case of mumps to the school health ser- vice between 01/09/1995 and 30/06/1996. All pupils in the affected schools were given a questionnaire on the symp- toms of mumps, visits to health care providers, possible contacts with other mumps cases, and history of vaccina- tion and mumps disease. The questionnaire was to be filled in by the parents retrospectively and returned by the end of June 1996. Vaccination data were thoroughly checked and compared against immunization data from the medical files 0264-410X/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.vaccine.2004.02.001