[An outbreak of mumps in a high school: Estimation of vaccine effectiveness. Zaragoza 2011]

Abstract

Introduction: Mumps outbreaks continue to occur, even after the consolidation of vaccination programs. An outbreak of mumps occurred in a high school in Zaragoza during December 2011.

Objective: To describe the outbreak and estimate vaccine effectiveness.

Case definition: unilateral or bilateral swelling of the parotid or other salivary glands for three or more days without any other apparent cause.

Reference population: People attending the 'Parque Goya' High School or with transmission chain origin in the High School.

Outbreak period: From two days before the onset of symptoms of the first case to five days after the last case. Samples were collected for virus confirmation (IgM, urine culture and oropharyngeal exudate), and isolates were processed for genotyping. A retrospective cohort study was performed in two high school classrooms to estimate vaccine efficacy. Public health authorities conducted active surveillance, isolation of cases, and vaccination of susceptible contacts.

Results: There were 27 cases. Twenty-one (77.8%) were vaccinated with two doses of Measles-Mumps-Rubella vaccine. Twelve (44%) were confirmed microbiologically. G1 genotype was determined in six cases. According to the cohort study, vaccine efficacy for one dose was 34% (95%CI: -44 to 70), and was 67% (95%CI: 28 to 83) for two doses.

Conclusions: Vaccine effectiveness was lower than expected. Early detection and isolation of cases have been instrumental in preventing new cases in schools.

Keywords: Brotes de enfermedades; Disease outbreaks; Efectividad; Effectiveness; Epidemiological surveillance; Mumps; Mumps vaccine; Parotiditis; Vacuna parotiditis; Vigilancia epidemiológica.