Epidemiology of a Mumps Outbreak In a Highly Vaccinated Population In Orange County, New York, 2009-2010, and Impact of the 3rd Dose MMR Intervention

Background: During June 2009–June 2010, approximately 3500 mumps cases were reported to CDC, primarily among Orthodox Jewish communities in the northeast, the largest outbreak in United States since 2006. In Orange County (OC), New York, mumps cases occurred primarily among students attending three Orthodox religious schools with high 2-dose measles, mumps and rubella (MMR) vaccine coverage.

Objectives: Describe the epidemiology of the outbreak in this community in OC and evaluate the impact of a 3rd dose of MMR for outbreak control.

Methods: Epidemiologic, clinical, and vaccination information was collected for mumps cases in OC. Because most cases were among school-aged children with reported 2 doses of MMR, a 3rd dose was offered to eligible 6th–12th grade students from January 19–February 2, 2010 (intervention period). Eligibility was defined as no prior history of mumps or receipt of a 3^rd dose of MMR. We calculated attack rates (AR) by age group during the 4 weeks pre-intervention (pre) and 4 weeks post-intervention (post).

Results: By June 30, 2010, 790 mumps cases had been reported in OC; 43% were among 11-17 years old when compared to 26% among 5-10 years old and 15% among 18-24 years old. Of the 790 cases, 64% were males with 6% orchitis reported among post-pubertal males. Of 658 cases with known vaccination status, 84% had received 2 doses of MMR. Of 2,255 eligible students, 83% received the 3rd dose. Among 6th–12th graders the AR declined from 20.8/1,000 (pre) to 0.7/1,000 (post) (p<0.05).

Conclusions: This is the first study to assess the impact of a 3^rd dose of MMR on transmission of mumps in an outbreak setting. Declines in post-intervention AR suggest that the 3rd dose of MMR may have had an impact in this outbreak but further analysis and studies are needed.