Mumps outbreak continues in NY/NJ

Friday's issue of MMWR included a report on the ongoing mumps outbreak in the New York metropolitan area. Nearly 1,500 cases have been identified thus far in Brooklyn and nearby counties; 97% of those infected are members of Orthodox Jewish communities.

Unlike many reports of disease outbreaks among religious groups, vaccine refusal is not a significant contributor to the outbreak. According to the MMWR report, 88% of those infected had received at least one dose of the combined MMR vaccine and 75% had received two doses, with higher percentages found among the younger age groups in which most cases have occurred. This illustrates the long-known fact that the mumps vaccine (like any vaccine) is less than 100% effective at preventing disease. High vaccination rates among communities provide additional protection through "herd immunity," but outbreaks such as this invariably will occur, public health officials explain.

As for what may be contributing to the spread of cases in this particular outbreak, an editorial note explains:

"...prolonged, close contact among persons might be facilitating transmission. Within the affected religious community, cases have occurred predominantly among school-aged boys, who attend separate schools from girls. The higher rate among boys might be a result of the additional hours that boys in this community spend in school compared with girls, including long periods in large study halls, often face-to-face with a study partner."

The report adds that larger family sizes among the affected community and fairly limited interaction with those outside it (even those in nearby neighborhoods and counties) might further explain the scope and limits of the outbreak.

Here is additional coverage from the Associated Press, NY1, and the New York City Department of Health, which is organizing free MMR vaccination clinics for those in the affected communities with incomplete vaccination histories.