Mumps outbreak among vaccinated university students associated with a large party, the Netherlands, 2010

We investigated a mumps outbreak within a highly vaccinated university student population in the Netherlands by conducting a retrospective cohort study among members of university societies in Delft, Leiden and Utrecht. We used an online questionnaire asking for demographic information, potential behavioural risk factors for mumps and the occurrence of mumps. Vaccine status from the national vaccination register was used. Overall, 989 students participated (20% response rate). Registered vaccination status was available for 776 individuals, of whom 760 (98%) had been vaccinated at least once and 729 (94%) at least twice. The mumps attack rate (AR) was 13.2% (95%CI 11.1–15.5%). Attending a large student party, being unvaccinated and living with more than 15 housemates were independently associated with mumps ((RR 42 (95%CI 10.1–172.4); 3.1 (95%CI 1.7–5.6) and 1.8 (95%CI 1.1–3.1), respectively). The adjusted VE estimate for two doses of MMR was 68% (95%CI 41–82%). We did not identify additional risk factors for mumps among party attendees. The most likely cause of this outbreak was intense social mixing during the party and the dense communal living environment of the students. High coverage of MMR vaccination in childhood did not prevent an outbreak of mumps in this student population.

► We investigated a mumps outbreak among university students in three Dutch cities.
► The attack rate was 44% in unvaccinated and 13% in twice-vaccinated individuals.
► Attending a student party was the most important risk factor for acquiring mumps.
► Being unvaccinated and having over 15 housemates were also risk factors.
► Intense mixing at a party and dense communal living facilitated mumps virus spread.