What's Likely Behind the Disneyland Measles Outbreak

Low vaccination rates may be to blame for increase in measles cases and recent Disneyland outbreak

/ Author:  / Reviewed by: Beth Bolt, RPh Joseph V. Madia, MD

(RxWiki News) Disneyland, “The Happiest Place on Earth,” became ground zero for a measles outbreak last December, and some experts say they know the cause.

Using data from the outbreak, the authors of a new study found that low vaccination rates might have led to the recent increase in measles cases.

“Given the highly contagious nature of measles, vaccination rates of 96% to 99% are necessary to preserve herd immunity and prevent future outbreaks,” the authors, led by Maimuna S. Majumder, MPH, of Boston Children’s Hospital, wrote.

These researchers estimated that only 50 to 86 percent of the Disneyland visitors were vaccinated against measles at the time of the outbreak.

The outbreak at Disneyland started between December 17 and 20, 2014.

Measles is a virus that causes fever, coughing and rashes. For people with weak immune systems, it can be a life-threatening illness.

Measles outbreaks are rare because most children are vaccinated against the virus through the measles, mumps and rubella (MMR) vaccine at 12 months. High vaccination rates create “herd immunity,” which makes it harder for viruses to spread from person to person.

But measles is highly contagious, so if a large number of children go unvaccinated, it can spread quickly.

“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,” Majumder and team wrote.

This research letter was published March 16 in JAMA Pediatrics.

The National Library of Medicine funded this research. The authors disclosed no conflicts of interest.

Review Date: 
March 13, 2015
Last Updated:
March 17, 2015