Mumps outbreak in a highly vaccinated school population. Evidence for large-scale vaccination failure
J. E. Cheek, R. Baron, H. Atlas, D. L. Wilson and R. D. Crider Jr
Division of Field Epidemiology, Centers for Disease Control and Prevention, Atlanta, GA, USA.
OBJECTIVES: To describe an outbreak and to identify risk factors for mumps
occurring in a highly vaccinated high school population. (Note: Highly
vaccinated means a population in which more than 95% have been vaccinated.)
DESIGN AND PARTICIPANTS: Survey and cohort study of 307 (97%) of 318
students. OUTCOME MEASURES: Mumps was defined as an illness with 2 or more
days of parotid swelling. Serologic confirmation of infection was obtained
in eight cases, seven of which were evaluated for presence of IgM antibody
using immunofluorescent antibodies. Vaccination records were verified for
297 (97%) students. RESULTS: Between October 3 and November 23, 1990,
clinical mumps developed in 54 students (attack rate, 18%), 53 of whom had
been vaccinated. Most cases (40 [77%] of 52) occurred 12 to 20 days after a
school-wide pep rally. Immunofluorescent antibody testing of all seven
specimens demonstrated IgM antibody to mumps. Risk factors for clinical
mumps identified in multivariate analyses included female gender (odds
ratio, 3.0; 95% confidence interval, 1.6 to 5.7) and source of vaccination
other than the local public health clinic (students vaccinated by private
providers [odds ratio, 3.0; 95% confidence interval, 1.3 to 5.2] or in
other districts [odds ratio, 2.4; 95% confidence interval, 1.1 to 5.3]).
CONCLUSIONS: The overall attack rate is the highest reported to date (and
to our knowledge) for a population demonstrating virtually complete mumps
vaccine coverage. Even verified documentation of vaccination may not be an
accurate indicator of an individual's protection against mumps. Vaccination
failure may play an important role in contemporary mumps outbreaks. We
found no evidence to indicate that waning immunity (secondary vaccine
failure) contributed significantly to this outbreak. A second dose of mumps
vaccine, as recommended using measles-mumps-rubella vaccine, could
potentially prevent similar outbreaks in secondary school populations in
the future.
