Demographic Distribution of Measles, Mumps, and Rubella (MMR) Vaccine Given in Mass Clinics during An Outbreak in Arizona in 2008

Background:
Measles was eliminated in the United States in 2000, but sporadic cases due to importations still occur, primarily in unvaccinated populations. In 2008, a community-wide outbreak of measles occurred in Pima County with 18 cases identified (14 confirmed, 4 epi-linked). As part of the outbreak response, over 8,000 contact investigations were conducted in multiple settings and control methods, including vaccination clinics, were implemented.

Setting:
Vaccine clinics in Pima County.

Population:
Residents of Pima County vaccinated by the Pima County Health Department (PCHD) and reported to the Arizona Department of Health Services (ADHS) through the Arizona State Immunization Information System (ASIIS).

Project Description:
Mass vaccine clinics were held in three communities starting April 9th to May 31st in 2008. Using ASIIS, the demographics of individuals vaccinated during the outbreak response were compared with vaccinations reported during the same time period in 2007.

Results/Lessons Learned:
During the outbreak, from February 19th to July 21st, 16,026 individuals were vaccinated with 17,307 doses of MMR. The median age of persons vaccinated was 43.1 years which was higher than the median age during the same period in 2007 (5.0 years). During the outbreak, 14,191 (82%) doses were administered to individuals over the age of 20, compared with 327 (21%) in 2007. Of the adults vaccinated during the outbreak, 1,986 doses (14%) were administered to individuals over the age of 65. Compared with 2007 data, there was a dramatic increase in the number of adults vaccinated against measles during the outbreak. According to the Advisory Committee on Immunization Practices (ACIP) guidelines, the majority of these individuals were likely immune to measles. Since resources available for outbreak control are limited, vaccine efforts and public information should focus on persons based on risk of infection or susceptibility utilizing epidemiologic data rather than targeting the entire community.