An analysis of publicly available outbreak data suggests that substandard vaccination compliance is likely to blame for the recent measles outbreak linked to Disneyland in California, according to an article published online by JAMA Pediatrics.

Without vaccination, measles is highly contagious. The recent outbreak started in December 2014, although the index case has not yet been identified. The rapid growth of cases indicates that a substantial percentage of the exposed population may be susceptible to measles infection due to lack of, or incomplete, vaccination, according to information in the research letter.

Maimuna S. Majumder, M.P.H., of Boston Children's Hospital and the Massachusetts Institute of Technology, Boston, and coauthors assessed the role of suboptimal vaccination coverage in the population by analyzing outbreak data.

The authors estimate that measles, mumps and rubella (MMR) vaccination rates among the exposed population where secondary cases occurred might be as low as 50 percent and likely no higher than 86 percent. Because measles is highly contagious, vaccination rates of 96 percent to 99 percent are necessary to preserve herd immunity and to prevent future outbreaks, according to the study.

"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," the research letter concludes.

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(JAMA Pediatr. Published online March 16, 2015. doi:10.1001/jamapediatrics.2015.0384. Available pre-embargo to the media at http://media. jamanetwork. com .)

Editor's Note: This work was supported by a grant from the National Library of Medicine. Please see article for additional information, including other authors, author contributions and affiliations, etc.

Media Advisory: To contact corresponding author Maimuna S. Majumder, M.P.H., call Keri Stedman at 617-919-3110 or email keri.stedman@childrens.harvard.edu.