A new study of a big mumps outbreak in 2006 raises questions about whether a new vaccine or another booster shot is needed.
The outbreak was the biggest in the United States since shortly before states began requiring two vaccine shots for youngsters in 1990.
Nearly 6,600 people became sick with the mumps, mostly in eight Midwest states, and the hardest-hit group was college students ages 18 to 24. Of those in that group who knew whether they had been vaccinated, 84 percent had received two mumps shots, according to the study by the Centers for Disease Control and Prevention and state health departments.
That "two-dose vaccine failure" startled public health experts, who hadn't expected immunity to wane so soon — if at all.
The mumps virus involved was a relatively new strain in the United States, not the one targeted by the vaccine, although there's evidence from outbreaks elsewhere that the shots work well against the new strain.
The researchers, reporting in today's New England Journal of Medicine, note that the virus probably came from travelers or students from the United Kingdom, where mumps shots are voluntary and where there was a much larger mumps outbreak of the same strain.
"If there's another outbreak, we would evaluate the potential benefit of a third dose to control the outbreak," said Dr. Jane Seward, a researcher with the CDC's viral diseases division.
The only U.S. vaccine, made by Merck & Co. of Whitehouse Station, N.J., hasn't been changed since its introduction in 1967, and there are no plans to change it, a Merck official said.
Dr. William Schaffner, head of preventive medicine at Vanderbilt University School of Medicine, said what's needed is a longer-lasting shot.
"We need a better vaccine," he said.