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TPDN 1989, Vol. 49, No. 30
two consecutive years (1986 and 1987). Persons
>15 years of age accounted for more than one
third of the reported total between 1985 and
1987; in 1967-1971, an average of only 8% of
reported cases occurred among this population.
Although reported mumps incidence increased in
all age groups from 1985 to 1987, the most
dramatic increases were among 10- to 14-year-
olds (almost a sevenfold increase) and 15- to 19-
year-olds (more than an eightfold increase).
The increased occurrence of mumps in suscep-
tible adolescents and young adults has been
demonstrated in several recent outbreaks in high
schools and on college campuses and in occupa-
tional settings. Nonetheless, despite this age shift
in reported mumps, the overall reported risk of
disease in persons 10-14 and >15 years of age is
still lower than that in the prevaccine and early
postvaccine era.
Consistent with previous findings, reported inci-
dcnce rates are lower in states with comprehen-
sive school immunization laws. The District of
Columbia and 14 states that routinely reported
mumps cases in 1987 had comprehensive laws
that require proof of immunity against mumps
for school attendance from kindergarten through
grade 12 (K-12). In these 15 areas, the incidence
rate in 1987 was 1.1 mumps cases per 100,000
population. In contrast, among the other states
that routinely reported mumps cases in 1987,
mumps incidence was highest in the 14 states
without requirements for mumps vaccination
(11.5 cases per 100,000 population), and interme-
diate (6.2 cases per 100,000 population) in the
18 states with partial vaccination requirements
for school attendance (ie, those that include
some children but do not comprehensively in-
clude K-12). Furthermore, the shift in age-
specific risk noted above occurred only in states
without comprehensive K-12 school vaccination
requirements.
Both the shift in risk to older persons and the
relative resurgence of reported mumps activity
noted in recent years are attributable to the
relatively underimmunized cohort of children
born between 1967 and 1977. There is no evidence
of waning immunity in vaccinated persons. During
1967-1977, the risk of exposure to mumps de-
clined rapidly even though vaccination of
children against mumps was only gradually being
accepted as a routine practice. Simultaneously,
mumps vaccine coverage did not reach levels
>50% in any age group until 1976 (5- to 9-year-
olds); in persons 15-19 years old, vaccine cover-
age did not reach these levels until 1983. This lag
in coverage relative to measles and rubella vac-
cines reflects the lack of an ACIP recommenda-
tion for routine mumps vaccine until 1977 and
the lack of emphasis in ACIP recommendations
on vaccination beyond toddler age until 1980.
These facts and the observed shift in risk to older
persons in states without comprehensive mumps
immunization school laws provide further evi-
dence that a failure to vaccinate, rather than
vaccine failure, is primarily responsible for the
recently observed changes in mumps occurrence.
MUMPS VIRUS VACCINE
A killed mumps virus vaccine was licensed for
use in the US from 1950 through 1978. This
vaccine induced antibody, but the immunity was
transient. The number of doses of killed mumps
vaccine administered between licensure of live
attenuated mumps vaccine in 1967 until 1978 is
unknown but appears to have been limited.
Mumps virus vaccine* is prepared in chick-
embryo cell culture. More than 84 million doses
were distributed in the United States from its
introduction in December 1967 through 1988.
The vaccine produces a subclinical, noncommu-
nicable infection with very few side effects.
Mumps vaccine is available both in monovalent
(mumps only) form and in combinations: mumps-
rubella and measles-mumps-rubella (MMR) vac-
cines.
The vaccine is approximately 95% efficacious
in preventing mumps disease; >97% of persons
known to be susceptible to mumps develop meas-
urable antibody following vaccination. Vaccine-
induced antibody is protective and long-lasting,
although of considerably lower titer than anti-
body resulting from natural infection. The dura-
tion of vaccine-induced immunity is unknown,
but serologic and epidemiologic data collected
during 20 years of live vaccine use indicate both
the persistence of antibody and continuing pro-
tection against infection. Estimates of clinical
vaccine efficacy ranging from 75% to 95% have
been calculated from data collected in outbreak
settings using different epidemiologic study
designs.
Vaccine Shipment and Storage
Administration of improperly stored vaccine
may fail to protect against mumps. During
storage before reconstitution, mumps vaccine
must be kept at 2-8 C (35.6- 46.4 F) or colder. It
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