Mumps found to have made alarming comeback in U.S.

BOSTON (Reuters) - Mumps made an alarming comeback in the United States in 2006 and may take years to completely eradicate, federal health experts reported on Wednesday.

The outbreak of the viral disease came despite the widespread use of a second dose of a mumps vaccine, produced by Merck, beginning in 1990.

Eighty-four percent of the people between the ages of 18 and 24 who became ill in the outbreak had received the second recommended dose, the researchers reported in the New England Journal of Medicine.

"A more effective mumps vaccine or changes in vaccine policy may be needed to avert future outbreaks and achieve the elimination of mumps," Gustavo Dayan of the Centers for Disease Control and Prevention in Atlanta and colleagues wrote.

There were no deaths from the virus, which can be as mild as a fever and swollen glands, or severe enough to cause deafness, testicular inflammation and encephalitis. But there were 6,584 cases nationwide and 85 hospitalizations, most concentrated in eight midwestern states and on college campuses.

"It would have been tens of thousands of cases if we didn't have the coverage," said Jane Seward, deputy director of the CDC's division of viral diseases.

The U.S. has a goal of eliminating the disease by 2010, but doctors consider a disease eliminated if there are no new home-grown cases over a 12-month period, Seward said in a telephone interview.

Thus, the goal might be achievable. But permanently banishing the disease is unlikely because 43 percent of nations do not vaccinate against the disease.

"Until the globe gets rid of their disease, we're at risk for importation and will continue to have outbreaks," Seward said.

A double dose of the vaccine is supposed to be 88 to 95 percent effective.

"The 2006 outbreak was the first account of a large-scale mumps epidemic characterized by two-dose vaccine failure," Dayan's team wrote.

"Although there was no single explanation for the outbreak, multiple factors may have contributed, including waning immunity, high population density and contact rates in colleges, and incomplete vaccine-induced immunity to wild virus."

Even countries that protect their children against mumps do not give two doses or have not been doing it for as long as the United States, Seward said.

That is one reason why there was an outbreak of more than 70,000 cases in Britain from 2004 to 2006, even though the population is one-fifth the size of the U.S. population.

Some advocacy groups have also expressed fears about the safety of the combined measles, mumps and rubella (MMR) vaccine, with some parents refusing to get their children vaccinated, officials say.

Health experts say these fears are ungrounded and say parents who do not vaccinate their children put them at risk and also children too young to have been vaccinated or with condition that prevent vaccination.

(Editing by Maggie Fox and David Wiessler)