[Study of a population-wide epidemic outbreak of mumps virus G1 in Jerez de la Frontera (Spain)].

Objectives: To characterize the mumps outbreak, assess the effectiveness of vaccines and discuss prevention and control measures.

Design: Observational cross-sectional study of cases by person, place, and time.

Location: City Jerez de la Frontera and 8 Primary Care centres.

Participants: A total of 116 cases of mumps were reported throughout seven months, with the last case in June 2008.

Main Outcomes: age, sex, place of study or work, symptoms start date, clinical description, complications, and genotype of virus isolation, history and vaccination compositions. Calculation of total vaccine effectiveness. Active case finding and contact studies were performed on the families, work places and leisure areas.

Results: The mean age of the cases was 16.24 years(SD 10.6). The majority (68.96%) of the cases were children at school and 31.03% arose from family and work areas. Mumps vaccine coverage rates were above 90%. The complete vaccine effectiveness (2 doses); for those under 20 years-old it was: 99.84% (95% CI=99.77 - 99.89), being lower in schools with the highest attack rate, immunised with current vaccine from Jeryl Lynn strain: 71.01% (95% CI=55.85 80.97). Two doses of this strain were used in 13.79% of the cases. Susceptible populations were vaccinated at the start of the outbreak: 11,381 doses used in schools and 93 outside schools.

Conclusions: An outbreak of mumps virus G 1 population with high rates of mumps vaccine coverage, with areas with low vaccine effectiveness with current vaccine. Mass vaccination of population has contributed to the resolution of the outbreak.