WEDNESDAY, April 9, 2008 (HealthDay News) -- In 2006, the largest U.S. outbreak of mumps in 20 years swept across eight Midwestern states, but a new study claims things could have been much worse.
The scope of outbreak was limited, because the number of people in the United States who have been vaccinated against mumps is very high, explained study co-author Amy A. Parker, from the U.S. Centers for Disease Control and Prevention.
There were total of 6,584 cases scattered across Illinois, Iowa, Kansas, Minnesota, Missouri, Nebraska, South Dakota and Wisconsin. Eighty-five people were hospitalized, but fortunately there were no deaths. However, 11 people lost their hearing and 22 developed meningitis, according to the report in the April 10 issue of the New England Journal of Medicine.
"The outbreak affected mostly college-age students who had two doses of the mumps vaccine," Parker said. "If that vaccination coverage drops, and a case of mumps is imported, then the spread can occur like wildfire."
Currently, mumps is not well-controlled around the world, Parker noted. "At the time of this outbreak, the United Kingdom was having an outbreak, and they saw over 70,000 cases of mumps," she said. "Most of these cases were among people who were not vaccinated."
In the United States, the mumps vaccine is part of the combination vaccine that includes mumps, measles and rubella (MMR). The vaccination rate against mumps in this country is robust: About 87 percent of adolescents have had two doses of the mumps vaccine, and more than 90 percent of 1-year-olds have had one dose.
"So, even though our outbreak was large, it wasn't of the same proportion as the one in the U.K.," Parker said.
She noted that the strain of mumps in the United Kingdom was identical to the one that spread across the United States. "It's likely this was the source, because the strains matched," she said.
Since the 2006 outbreak, there hasn't been another of the same proportion in the United States, Parker added.
However, the CDC has set a goal of eliminating mumps in the United States by 2010. Although the current vaccine was able to limit the scope of the outbreak, it is only 90 percent effective after two doses, Parker said. "So, even if you had a 100 percent vaccination rate, you would still have 10 out of every 100 people susceptible to mumps," she explained.
To protect people from future outbreaks and reach the 2010 goal, Parker thinks changes in the vaccine to make it more effective or booster shots to preserve immunity should be considered.
One expert thinks the having children vaccinated against mumps is the best way to prevent future outbreaks.
"Since the mumps vaccine was introduced in 1967, there was a dramatic decline in the incidence of mumps not only in our country but in many other countries," said Dr. Paul A. Offit, director of the Vaccine Education Center and chief of infectious diseases at Children's Hospital of Philadelphia.
Offit agrees that the high rate of vaccination kept the outbreak small, and he doesn't expect to see a similar outbreak anytime soon. But he recommends that children get the full two doses of the MMR vaccine.
However, Offit doesn't think the 2006 outbreak is reason enough to change the current two-shot vaccine policy. "It's been two years since the outbreak, and there hasn't been a similar outbreak. So, I don't think any changes in vaccine policy need to be made at this time, because it will be based on a single outbreak," he said.
But not getting vaccinated at all is taking a risk, Offit said. "The choice not to get vaccinated is not a risk-free choice. It's just a choice to take a different risk," he said. "I think the choice not to get a vaccine for a child is a bad one. Mumps is not a benign disease."
While mumps in children is usually mild, complications can include loss of hearing, meningitis and encephalitis, which can be fatal. In adult men, mumps can result in sterility.
For more on mumps, visit the U.S. Centers for Disease Control and Prevention.