JAMA Pediatrics
March 2015, Vol 169, No. 3
http://archpedi.jamanetwork.com/issue.aspx
[Reviewed earlier]

Online First
Research Letter| March 16, 2015
Substandard Vaccination Compliance and the 2015 Measles Outbreak ONLINE FIRST
Maimuna S. Majumder, MPH1,2; Emily L. Cohn, MPH2; Sumiko R. Mekaru, DVM, PhD2; Jane E. Huston, MPH2; John S. Brownstein, PhD2,3
Author Affiliations
JAMA Pediatr. Published online March 16, 2015. doi:10.1001/jamapediatrics.2015.0384

The ongoing measles outbreak linked to the Disneyland Resort in Anaheim, California, shines a glaring spotlight on our nation’s growing antivaccination movement and the prevalence of vaccination-hesitant parents. Although the index case has not yet been identified, the outbreak likely started sometime between December 17 and 20, 2014.1,2 Rapid growth of cases across the United States indicates that a substantial percentage of the exposed population may be susceptible to infection due to lack of, or incomplete, vaccination. Herein, we attempt to analyze existing, publicly available outbreak data to assess the potential role of suboptimal vaccination coverage in the population.

…Discussion
This preliminary analysis indicates that substandard vaccination compliance is likely to blame for the 2015 measles outbreak. Our study estimates that MMR vaccination rates among the exposed population in which secondary cases have occurred might be as lowas50% and likely no higher than 86%. Given the highly contagious nature of measles, vaccination rates of 96% to 99% are necessary to preserve herd immunity and prevent future outbreaks.3 Even the highest estimated vaccination rates from our model fall well below this threshold. While data on MMR vaccination rates are available, coverage is often calculated at the state or county level and may not be granular enough to assess risk in an outbreak situation; this is especially the case for outbreaks originating at a tourist destination, where vaccination coverage among visitors is highly heterogeneous. Clearly, MMR vaccination rates in many of the communities that have been affected by this outbreak fall below the necessary threshold to sustain herd immunity, thus placing the greater population at risk as well.