MONDAY, Nov. 5, 2012 (HealthDay News) -- Adding a third dose of mumps vaccine may have helped quell a mumps outbreak in a close-knit religious community in New York in 2009 and 2010, according to new research.
Investigators said three-quarters of the infected people had already received the recommended two doses of the childhood measles-mumps-rubella (MMR) vaccine.
Because the village was already relatively isolated, public health officials had few options to contain the outbreak other than administering a third dose of the vaccine, said study co-author Dr. Preeta Kutty, a medical epidemiologist with the division of viral diseases at the U.S. Centers for Disease Control and Prevention in Atlanta.
The rate of new cases slowed down shortly afterward, according to the study, which was published online Nov. 5 in the journal Pediatrics.
The outbreak started when an Orthodox Jewish boy developed mumps after returning to his community in New York, following a visit to Britain.
The boy attended an Orthodox Jewish summer camp, where another 25 cases developed. And when those individuals returned to their homes, the outbreak spread further, ultimately infecting nearly 400 people in Orange County, N.Y.
After receiving special approval, researchers gave a third dose of MMR to nearly 1,800 sixth- to twelfth-graders at local schools who had already had the initial two doses.
After the third shot, the mumps rate in this group declined by 96 percent -- from 4.93 percent of students prior to the vaccination to 0.13 percent after.
In the village overall, mumps declined by almost 76 percent after the third dose was administered to this select group of students, suggesting that the intervention conferred a "herd-immunity" effect. When enough people in a community are immunized, this tends to protect others in the community, even those who aren't vaccinated.
The researchers did not note any major side effects.
The authors did note that the third dose of MMR was given after the outbreak had peaked, raising the possibility that the decline in cases would have happened without the third vaccination.
The authors also emphasized that even though giving a third dose of the vaccine may have mitigated the outbreak, they are not advocating that a third dose be routinely given.
Nor do they want the public to think two doses of MMR is not protective, Kutty said.
There were some unusual circumstances in this situation, namely the intense contact people had with one another, she said.
A study appearing earlier this week in the New England Journal of Medicine pointed out that Orthodox Jewish people tend to cluster geographically and socially. Boys spend a great deal of time in religious schools called yeshivas, sometimes working with a partner face-to-face for hours at a time.
Also, households in this community are larger than usual -- 5.7 people per home on average compared to the national average of 2.6, according to the Pediatrics study.
Dr. Gloria Riefkohl, a pediatrician at Miami Children's Hospital, said that because mumps is highly contagious, this may have helped create a "perfect storm."
The first dose of mumps vaccine is given as part of the MMR vaccine between 12 and 15 months of age, and the second is given between the ages of 4 and 6.
Immunity can wane over time, said another expert, Dr. Kenneth Bromberg, chairman of pediatrics and director of the Vaccine Study Center at the Brooklyn Hospital Center in New York City. Also, the mumps vaccine may be less effective than the two other vaccines contained in the same shot, he said.
That makes using a third shot in outbreak situations something else to "add to the armamentarium," he said.
In most children, mumps is generally mild, but serious problems, including deafness, can result. In rare cases, children can die.
The U.S. Centers for Disease Control and Prevention has more on mumps.