Vaccine not fail-safe in ongoing mumps outbreak

In a recent mumps outbreak occurring in the eastern United States, even some of those who were vaccinated against the infectious illness got sick, health officials report according to HealthDay News.

A study released Feb. 11 by the U.S. Centers for Disease Control and Prevention tracked an ongoing outbreak of mumps, largely confined to an orthodox Hasidic Jewish group. The outbreak started among boys attending a religious summer camp in New York State and continued when the youngsters returned to their homes in New York and New Jersey. Currently some 1,521 cases have been reported, with more individuals coming down with the disease.

The report is published in the Feb. 12 edition of the CDC's Morbidity and Mortality Weekly Report.

Mumps is a “self-limiting disease” with no specific treatment. It is best treated with bed rest and over-the-counter medications such as acetaminophen to reduce fever, according to the CDC.

Most of the people who have become sick had received the mumps, measles and rubella vaccine, according to the report. In fact, 88 percent had received at least one dose of the vaccine and 75 percent had received two doses.

However, the vaccine is not 100 percent effective, the CDC team noted. Studies have found one dose 73 percent to 91 percent effective, while the effectiveness of two doses ranged from 79 percent to 95 percent, according to the report.

"That means if you were to expose 100 people to mumps, 10 of them might still come down with the disease," said study co-author and CDC epidemiologist Kathleen Gallagher. In this outbreak, these percentages are holding, she added.

Although the vaccine doesn't protect everyone, it does work for most people and effectively prevents outbreaks from becoming worse. "We think that if we didn't have such high levels of MMR coverage, we would have even more spread," Gallagher said.

Outbreaks of mumps are not all that unusual, Gallagher said.

"We have had outbreaks of mumps in communities that have had two doses before," she said. In 2006, there was a large outbreak of mumps among college students in the Midwest, she noted.

And mumps remains prevalent in other areas of the world.

"While we are well-vaccinated against mumps in the United States, many countries throughout the world don't vaccinate at all against mumps," she said. "There is a lot of mumps circulating globally. This means that anytime there is a potential for importation like happened with this summer camp, there is potential for mumps to be introduced even into a highly vaccinated population."