November 05, 2012
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Intense exposure likely led to mumps outbreak among Orthodox Jewish boys

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An outbreak of mumps among Orthodox Jewish boys from 2009 to 2010 likely occurred because of intense exposure to the virus that led to decreased protection afforded by the vaccine, researchers reported in The New England Journal of Medicine.

The outbreak began with an 11-year-old boy who developed parotitis on June 28, 2009, while he was attending a camp with about 400 other Orthodox Jewish boys. The boy had recently returned from the United Kingdom, where there was an ongoing mumps outbreak. Throughout the camp, 25 cases of mumps developed among 22 campers and three adults.

The virus then spread through New York City, Rockland and Orange counties in New York and Ocean County in New Jersey, when the infected campers returned home. The outbreak comprised 3,502 cases of mumps, of which 97% occurred among Orthodox Jewish people. In New York City, most cases were in three Orthodox Jewish neighborhoods. In the three counties, the cases were mostly in one or two villages. Among the 97 cases that were not among Orthodox Jewish people, all were linked to an Orthodox person because of work or community ties.

There were 2,317 who had a verified vaccination status: 76% had received two doses of the measles-mumps-rubella vaccine and 14% received one dose. Among adolescents aged 13 to 17 years with documented vaccination status, 89% had received two doses of the MMR vaccine. Of the affected patients aged 13 to 17 years, 78% were male.

The characteristics of the outbreak suggest that Orthodox Jewish schools for boys were the center of the transmission of the virus. In these schools, pairs of students intensely study religious texts together, face-to-face, with several pairs at a single table. This atmosphere may have provided for efficient transmission of mumps, and the intense exposure overcame vaccine-induced protection.

“The fact that the outbreak did not spread to surrounding communities highlights the effectiveness of the two-dose MMR vaccine schedule in most settings,” the researchers wrote. “Previous studies have shown that two doses of mumps vaccine have an effectiveness of approximately 88% in preventing clinical mumps, and this schedule has been successful in controlling mumps in the general US population.”

Disclosure: The researchers report no relevant financial disclosures.