Disney measles outbreak: Study blames low vaccination rates

The mathematical model estimates that in communities where the disease continued to spread, vaccination rates were well below the level needed to preserve herd immunity.
The mathematical model estimates that in communities where the disease continued to spread, vaccination rates were well below the level needed to preserve herd immunity. Photo by Redcorn Studios [Matt] via Flickr Creative Commons

The measles outbreak that started at the Disney theme parks in Anaheim most likely spread because of low vaccination rates, according to a statistical analysis by researchers at MIT and Boston Children’s Hospital.

The researchers work in the field of computational epidemiology. They devised a formula to estimate vaccination rates in the exposed population. 

While noting that their conclusions are based on a "preliminary analysis," the researchers said their mathematical model estimates that in communities where the disease continued to spread, vaccination rates were well below the level needed to preserve herd immunity. Rates could have been as low as 50 percent and likely no higher than 86 percent, 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 authors write.

According to the California Department of Public Health, 40 cases of measles were likely contracted at Disneyland and 30 more got infected through close contact with the original 40. An estimated 60 more cases are likely linked to the outbreak, the Department says.

For a highly contagious disease like measles, experts say at least 92 percent of a given population needs to be vaccinated to achieve herd immunity.

The study was published as a research letter in JAMA Pediatrics. 

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