2766. Identification and Description of Mumps Cases in a Non-Outbreak Setting and Evaluation of the Effectiveness of Mumps Containing Vaccines Over Time

BACKGROUND: Despite high coverage for 2 doses of MMR/MMRV vaccine, the United States and other countries have seen increases in outbreaks of mumps, mainly on college campuses and other close communities, which has been attributed to waning immunity to mumps. The objective of this study was to identify mumps cases within Kaiser Permanente Northern California, a large healthcare organization, and to assess waning of vaccine immunity against mumps in a non-outbreak setting. METHODS: Potential cases were identified by international classification of disease (ICD) 9 code 072, ICD 10 code B26 or by laboratory orders for mumps. We conducted medical chart reviews to confirm diagnoses, timing relative to vaccination and clinical characteristics. We selected cases and controls among KPNC born after 1988 who were members for ≥9 months before diagnosis or anchor date and who received their second dose at ages 4 to 6 years, matching cases with controls on geographical area. To assess for risk of mumps in relation to time since a second MMR/MMRV dose, we compared cases and controls using multivariable logistic regression adjusted for age, sex and calendar time of mumps diagnosis. RESULTS: Among 397 potential cases identified, chart review confirmed 178 (44.8%) as mumps. About half (87/178) were confirmed by both positive laboratory test and clinical diagnosis, with the remainder by clinical diagnosis alone. Median age at diagnosis for the 187 cases was 30 years (range 1 year–91 years). Most cases had parotitis (93%) and there were 7 cases of orchitis. The 34 cases with complete vaccination information were matched to 539,301 controls. The mean time since the second vaccine dose was shorter for cases compared with controls (6.5 years vs. 9.0 years, P = 0.008). After adjustment, there was no significantly increased risk of mumps associated with time since second MMR/MMRV dose (adjusted odds ratio = 1.08, 95% CI 0.57–2.05). CONCLUSION: In the setting of a large healthcare organization, our results do not provide evidence of waning immunity following 2 doses of MMR/MMRV; however, identifying and confirming mumps cases were challenging and analyses were limited by small number of cases. Large future studies will be needed to confirm whether risk of mumps increases over time in non-outbreak settings. DISCLOSURES: All authors: No reported disclosures.