659. Mumps Outbreak in a High School: Uptake and Parental Perceptions of Third Dose MMR Recommendations, Dallas County, Texas, 2017

BACKGROUND: In February 2017, a mumps outbreak was identified in a large Dallas high school among students who had previously completed the two-dose MMR vaccination series. Early notification of recommendations for third dose MMR and free vaccination clinics provided an opportunity to assess vaccine uptake, efficacy, and parental perceptions of third dose MMR recommendations. METHODS: Mumps illnesses were classified as probable or confirmed cases using 2012 CSTE case definitions. Information about vaccination status, exposure history, and illness characteristics was collected from case interviews and medical records. A third MMR vaccine was recommended to all noncase students and offered without charge at school-based vaccination clinics. Supplemental questionnaires assessing parental knowledge and attitudes regarding this third MMR recommendation were administered to guardians of a randomly selected sample of 20 students who received third dose MMR and 50 students who did not receive the vaccine. Fishers exact tests and chi-square were used to compare responses. Data analysis was performed using SAS 9.4. RESULTS: From February to May 2017, 28 PCR-confirmed and 12 probable mumps cases were identified in students attending one high school campus (24.3 cases per 1,000 students). Of the 1,646 enrolled students, 99.8% had documentation of at least two doses of MMR prior to the outbreak, including all mumps cases. Three undervaccinated students who declined to receive one dose of MMR were excluded from school during the outbreak. Following public health recommendations for a voluntary third MMR dose, 291 students (17.6%) elected to receive a third MMR. No mumps cases occurred in students who received a third vaccine dose. Parental perception of protective benefit of an additional third dose of MMR was significantly associated with decisions to receive third dose MMR (OR: 4.9; 95% CI = 1.6–15.3). CONCLUSION: Responsiveness to health department recommendations for third MMR vaccination in this outbreak setting was limited, even with broad educational communications and free school-based vaccine clinics. The challenges in achieving robust voluntary uptake of a third MMR dose may not improve substantially despite recent ACIP recommendations, in the absence of school mandates requiring third dose of MMR during outbreaks. DISCLOSURES: All authors: No reported disclosures.