Epidemic of mumps among vaccinated persons, The Netherlands, 2009-2012

Abstract

To analyze the epidemiology of a nationwide mumps epidemic in the Netherlands, we reviewed 1,557 notified mumps cases in persons who had disease onset during September 1, 2009-August 31, 2012. Seasonality peaked in spring and autumn. Most case-patients were males (59%), 18-25 years of age (67.9%), and vaccinated twice with measles-mumps-rubella vaccine (67.7%). Nearly half (46.6%) of cases occurred in university students or in persons with student contacts. Receipt of 2 doses of vaccine reduced the risk for orchitis, the most frequently reported complication (vaccine effectiveness [VE] 74%, 95% CI 57%-85%); complications overall (VE 76%, 95% CI 61%-86%); and hospitalization (VE 82%, 95% CI 53%-93%). Over time, the age distribution of case-patients changed, and proportionally more cases were reported from nonuniversity cities (p<0.001). Changes in age and geographic distribution over time may reflect increased immunity among students resulting from intense exposure to circulating mumps virus.

Keywords: MMR; epidemic; herd immunity; immunization; mumps; outbreaks; surveillance; the Netherlands; vaccination; vaccine; viruses.

Figure

Numbers of notified mumps cases, by week of onset, The Netherlands, September 1, 2009–August 31, 2012 (N = 1,557 cases). Seasons and number of cases (n) are indicated; black line indicates 3-week moving average.