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Intense exposure likely led to mumps outbreak among Orthodox Jewish boys
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.
Perspective
Back to TopWe now know that the mumps vaccine is not as good as we thought it was a decade or two ago. There are several reasons for this. When you look at vaccine efficacy when the vaccine was first available to the public, which was during a time period when you’re trying to get rid of the disease, chances are that a vaccinated person still would have been exposed to wild mumps virus circulating in the community. They wouldn’t have gotten sick, because they were vaccinated, but the natural exposure would have caused them to have a naturally boosted immunity. So, at that time, calculations of the vaccine efficacy can be higher than when the disease is gone and you’re relying totally on the vaccine-induced immunity.
Another thing is that the type of mumps they saw in New York was genotype G, which is what we also saw in the Iowa outbreak in 2006 and in the U.K. outbreak. The mumps vaccine is made with genotype A. It still gives pretty good cross protection. This is strictly a hypothesis, but it might be possible that that the A strain vaccine doesn’t give quite the same efficacy as it would have if it had a G strain vaccine.
When we had the outbreak here in Iowa, we also saw a lot of highly-vaccinated people getting mumps, but typically they were in a dormitory and college setting. In this setting, the amount of exposure to mumps might be higher than among older adults who have only limited close face-t-face interactions with large numbers of people. There is intense exposure among student in a college, like in the Iowa outbreak, or in the Orthodox Jewish schools like this particular outbreak. We also don’t see as much activity in the other populations, such as younger school children, probably because they received the vaccine more recently, so the vaccine is “fresher”, thus may be providing more immunity.
In this outbreak in Orthodox Jewish communities, they saw lower rates of serious complications than what one might have expected. We saw that in the Iowa outbreak also. I think that’s because the vaccine, though it doesn’t provide complete protection against all symptoms of mumps if infected, probably provided protection against the most serious complications.
They also found that the third dose seemed to provide better protection, probably because the third dose provides an increase in immunity. I don’t know if we’ll automatically go to recommending a third dose of mumps vaccine. But in places where the intensity of the exposure might be high, a third dose might help reduce transmission and stop the outbreak. Should we have another outbreak in Iowa, that is something I’d look at very seriously.