Low Vaccination Rates To Blame for Disneyland Measles Outbreak

Low vaccination rates likely were the cause of a measles outbreak that began at Disneyland in December 2014, according to research published on Monday in JAMA Pediatrics, NPR's "Shots" reports.

Background on Outbreak

As of Friday, California had confirmed 133 cases of measles in the state linked to the outbreak that began at Disneyland. Of those, at least 57 had not been vaccinated.

Measles was declared eliminated from the U.S. in 2000, but low vaccination rates and infected people entering the country from other areas have cause isolated, periodic outbreaks.

The measles-mumps-rubella, or MMR, vaccine is about 95% effective, according to "shots" (Hensley, "Shots," NPR, 3/16).

Details of Research

For the research, experts from Boston Children's Hospital and the Massachusetts Institute of Technology examined data on the California outbreak, historical information and other data points.

They found that the vaccination rate among individuals that were exposed to measles during the outbreak that began at Disneyland was between 50% and 86% -- far lower than the 96% vaccination rate required to maintain herd immunity.

The researchers wrote, "Clearly, MMR vaccination rates in many of the communities that have been affected by this outbreak fall well below the necessary threshold to sustain herd immunity, thus placing the greater population at risk as well."

Eric Handler -- public health officer for Orange County, where Disneyland is located -- said the findings "underscor[e] the importance of vaccination in preventing the spread of measles and protecting children who are too young to be vaccinated" (Kaplan, "Science Now," Los Angeles Times, 3/16).