Low Vaccination Rate Sparked Disneyland Measles Outbreak

The Disneyland measles outbreak is linked to vaccination rates being well below the heard immunity threshold, according to Boston University Hospital researchers.

The Disneyland measles outbreak is linked to vaccination rates being well below the heard immunity threshold, according to Boston University Hospital researchers.

Assessing the California Department of Public Health and HealthMap disease surveillance system’s case data, investigators noted the vaccination rate of case clusters in CA, AZ, and IL fell between 50 and 86 percent. For herd immunity to take effect, inoculation must occur at 96 to 99 percent.

“Rapid growth of [measles] 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,” the authors wrote in the JAMA Pediatrics study, published online on March 16.

Two of the study’s contributors, Maimuna Majumder, MPH, and John Brownstein, PhD, of Boston Children's Informatics Program, then determined the measles virus’ effective reproduction rate (RE) — which predicts how fast a virus will spread in a partially immunized community. In doing so, they reported measles’ RE at Disneyland was between 3.2 and 5.8.

“The ongoing measles outbreak linked to the Disneyland Resort in Anaheim, CA, shines a glaring spotlight on our nation’s growing antivaccination movement and the prevalence of vaccination-hesitant parents,” the investigators noted.

While their study does not determine vaccination rates in the US, CA, or in exposed Disneyland attendants, the authors claimed it “reflects the vaccination rate among the exposed populations in each cluster of cases linked to the outbreak so far.”

Brownstein said he hoped their findings encouraged families to ensure their vaccination status and offered insight to public health officials.

"Our data tell us a very straightforward story — that the way to stop this and future measles outbreaks is through vaccination," Brownstein said in a news release. "The fundamental reason why we're seeing the number of cases we are is inadequate vaccine coverage among the exposed.”