The United States experienced the largest mumps outbreak in almost
20 years during 2006 — one that quickly spread across states in the
In January 2006, health officials identified the first cases of
the mumps in colleges in eastern Iowa. By April 2006, the outbreak had reached
40 states and infected 2,786 people. The highest incidence occurred among
college students aged 18 to 24 years.
“There were a combination of factors that probably caused
this outbreak,” Patricia Quinlisk, MD, MPH, medical director and state
epidemiologist at the Iowa Department of Public Health and member of the
Infectious Disease News editorial advisory board, said in an
interview. “It appears that the two-dose mumps vaccine that was
administered to these students when they entered school about 12 years prior
may only be about 80% effective, and because respiratory and saliva-spread
disease like this are easier to spread in places like college dormitories. We
also think that some of the early cases may have not been diagnosed as mumps
since the disease had been rare in Iowa for about 20 years and because the
disease was not expected in vaccinated people.”
Reported mumps cases
Quinlisk and colleagues in other states and CDC officials
collected and reviewed mumps cases reported to the National Notifiable Diseases
Surveillance System from state health departments and reported their findings
in The New England Journal of Medicine. A patient with a confirmed
case of mumps met the clinical case definition and also had a positive
laboratory test or was epidemiologically linked. Probable cases were defined as
those that fit the clinical case definition but were not laboratory confirmed.
Data were then reviewed from the U.S. Immunization Survey, the
National Immunization Survey, the National Health Interview Survey and school
Case information included vaccination status and self-reported
race or ethnic groups for the eight states most affected: Illinois, Iowa,
Kansas, Minnesota, Missouri, Nebraska, South Dakota and Wisconsin. Four of the
states also included information on college attendance.
Results of the study indicated that 6,584 mumps cases were
reported in 2006; 85 people were hospitalized, and no deaths directly
attributed to mumps were reported.
Eighty-five percent of these college students with mumps lived in
the eight neighboring Midwestern states. Eighty-four percent of the 1,020
individuals aged 18 to 24 years with known vaccine status received both doses
of the mumps vaccine. “This is not surprising since almost all college
students have been vaccinated, with only 4% of those younger than 30 never
vaccinated,” said Quinlisk. “Thus it would be expected that higher
number of cases occur in those vaccinated students in whom immunity was not
sustained than in those who were never vaccinated.”
Waning immunity may be secondary to lack of natural exposure.
People aged 18 to 24 years were born in the 1980s when mumps activity was
sufficiently low and many of them were never exposed to the disease. A second
dose of the vaccine was probably administered during the 1990s, a time when
boosting from exposure to the natural virus became increasingly rare. These
Midwestern students entered college at a time of increased risk for the
importation of the mumps virus from other countries, such as the 2004 to 2006
outbreak in the United Kingdom that affected more than 70,000 people.
According to the researchers, incidence was higher among women
than among men (13.5 vs. 7.7 per 100,000 people). This was not explained by
differences in vaccination status or age. In response to this outbreak, the CDC
and the American College Health Association now recommend that colleges require
students to receive the two-dose measles-mumps-rubella vaccine (M-M-R II,
The study concluded that a more effective mumps vaccine or changes
in the vaccine policy may be needed to avert future outbreaks and achieve the
elimination of mumps.
Already, the Advisory Committee on Immunization Practices updated
their recommendations in (June 2006), which now advise eligible children and
health care workers to receive two doses of the mumps vaccine, separated by at
least 28 days. Jennifer Southall
For more information:
- Dayan G, Quinlisk P, Parker A, et al. Recent resurgence of
mumps in the United States. N Engl J Med. 2008;358:1580-1589.