Background and objective: We analysed a mumps outbreak that occurred in Navarre between August 2006 and December 2007, in which vaccinated persons were widely affected.
Patients and methods: Reports of mumps cases were completed by searching primary, emergency and hospital records and laboratory reports. Factors that could affect the occurrence of cases were analysed by birth cohort.
Results: A total of 2866 mumps cases were detected (attack rate 4.7/1000), with 61% of cases in men and a peak incidence at age 19 (inter-quartile range 16-25 years). 14% of cases were confirmed by laboratory: 59 by virus isolation, 14 by PCR and 333 by IgM. The G1 genotype was identified in 7 cases. 21% of cases had been born before 1980 (pre-vaccine cohorts), and 0.2% had not yet reached the vaccination age (15 months). In the cohorts born between 1980 and 2000 (with the opportunity for vaccination), 94.5% of cases had received at least one dose and 88.3%, two doses. 31% of cases occurred in cohorts vaccinated with a first (1995-1997) or second (1986-1988) dose of the Rubini strain. There was also a record of 772 cases who had received two doses of the Jeryl Lynn strain.
Conclusions: This widespread outbreak is explained by the concurrence of various factors. The current vaccine has substantially reduced the incidence of mumps, but appears unable to totally eliminate virus circulation.