374 | www.pidj.com The Pediatric Infectious Disease Journal • Volume 32, Number 4, April 2013
Background: Despite high 2-dose measles-mumps-rubella (MMR) vaccine
coverage, a large mumps outbreak occurred on the Us territory of Guam
during 2009 to 2010, primarily in school-aged children.
Methods: We implemented active surveillance in april 2010 during the
outbreak peak and characterized the outbreak epidemiology. We adminis-
tered third doses of MMR vaccine to eligible students aged 9–14 years in 7
schools with the highest attack rates (aRs) between May 18, 2010, and May
21, 2010. Baseline surveys, follow-up surveys and case-reports were used
to determine mumps aRs. adverse events postvaccination were monitored.
Results: Between December 1, 2009, and December 31, 2010, 505 mumps
cases were reported. self-reported pohnpeians and chuukese had the high-
est relative risks (54.7 and 19.7, respectively) and highest crowding indi-
ces (mean: 3.1 and 3.0 persons/bedroom, respectively). among 287 (57%)
school-aged case-patients, 270 (93%) had ≥2 MMR doses. a third MMR
dose was administered to 1068 (33%) eligible students. three-dose vac-
cinated students had an aR of 0.9/1000 compared with 2.4/1000 among
students vaccinated with ≤2 doses >1 incubation period postintervention,
but the difference was not significant (P = 0.67). no serious adverse events
Conclusions: this mumps outbreak occurred in a highly vaccinated popu-
lation. the highest aRs occurred in ethnic minority populations with the
highest household crowding indices. after the third dose MMR intervention
in highly affected schools, 3-dose recipients had an aR 60% lower than stu-
dents with ≤2 doses, but the difference was not statistically significant and
the intervention occurred after the outbreak peaked. this outbreak may have
persisted due to crowding at home and high student contact rates.
Key Words: mumps, outbreak control, third dose measles–mumps–rubella
intervention, vaccine preventable disease, immunization
(Pediatr Infect Dis J 2013;32: 374–380)
matic.1–3 severe complications include encephalitis,4 deafness5,6
and orchitis.7 Mumps vaccine was licensed in the United states in
1967 and recommended for routine use in 1977.8 a second dose
of measles–mumps–rubella (MMR) vaccine was recommended for
all school-aged children and select high-risk groups in 1989 for
measles prevention.9 Due to high 2-dose MMR vaccine coverage,
rates of reported mumps in the United states declined by over 99%
in 2005 compared with the immediate prevaccine era.10 annual
mumps incidence in the United states was approximately 1 case per
million population (0.9−1.2 per million/population) between 2000
and 2005.10 a mumps elimination goal was set for 2010.11
However, from 2006 to 2010, several large mumps out-
breaks occurred in primarily 2-dose vaccinated Us populations.
in 2006, 6584 reported cases occurred, mainly affecting Midwest-
ern college students. standard control measures (eg, isolation and
vaccine catch-up campaigns) were implemented for outbreak con-
trol.12 During 2009 to 2010, 3502 mumps cases were reported in a
highly 2-dose vaccinated population in an orthodox Jewish com-
munity in the northeast; this outbreak was the first to use a third
dose MMR vaccine intervention for outbreak control.13,14
on February 25, 2010, Guam Department of public Health
and social services (DpHss) was informed of a mumps case in
a 2-dose vaccinated 15-year-old male. More cases were subse-
quently reported, primarily among vaccinated school children
aged 9−14 years. the last reported mumps outbreak on Guam
occurred in 1958; in the past decade, Guam reported an average
of 4 mumps cases annually. as part of the public health response
to this outbreak, a third dose of MMR vaccine was administered.
We evaluated the outbreak epidemiology and the safety and impact
of a third dose MMR vaccine intervention in target populations for
umps is an acute, viral illness that classically manifests with
fever and parotitis; 15%–27% of infections are asympto-
Guam is a Us territory with a 2010 population of ~180,692
persons.15 the primary ethnicity on Guam is chamorro, comprising
37% of the population.15 Guam follows the advisory committee on
immunization practices recommendations for MMR vaccination:
the first MMR dose is administered at ages 12–15 months and the
second dose at 4–6 years.16
Mumps cases were classified according to the 2008 council
of state and territorial epidemiologists mumps case definition.17
on Guam, healthcare providers are mandated by law to report
copyright © 2013 by Lippincott Williams & Wilkins
Epidemiology of a Mumps Outbreak in a Highly Vaccinated
Island Population and Use of a Third Dose of Measles–Mumps–
Rubella Vaccine for Outbreak Control—Guam 2009 to 2010
George E. Nelson, MD,*† Annette Aguon,‡ Engracia Valencia,‡ Rita Oliva,‡ Michele Leon Guerrero,‡
Richard Reyes,‡ Anna Lizama,‡ Daryl Diras,‡ Annakutty Mathew, MD, FACP,‡§ E. Jessica Camacho, MEd,¶
Moryne-Nicole Monforte,¶ Tai-Ho Chen, MD,‖ Abdirahman Mahamud, MD,*† Preeta K. Kutty, MD, MPH,*
Carole Hickman, PhD,* William J. Bellini, PhD,* Jane F. Seward, MBBS, MPH,*
Kathleen Gallagher, MPH, DSc,** and Amy Parker Fiebelkorn, MSN, MPH*
accepted for publication october 17, 2012.
From the *national center for immunization and Respiratory Diseases; †epi-
demic intelligence service, centers for Disease control and prevention,
atlanta, Ga; ‡Guam Department of public Health and social services;
§Guam Memorial Hospital; ¶Guam Department of education, Guam; ‖Divi-
sion of Global Migration and Quarantine; and **office of surveillance,
epidemiology, and Laboratory services, centers for Disease control and
prevention, atlanta, Ga.
the findings and conclusions in this article are those of the authors and do not
necessarily represent the views of the centers for Disease control and pre-
the authors have no funding or conflicts of interest to disclose.
address for correspondence: amy parker Fiebelkorn, Msn, MpH, cDc/nciRD,
1600 clifton Rd, Ms a-34, atlanta, Ga 30333. e-mail: email@example.com.
The Pediatric Infectious Disease Journal • Volume 32, Number 4, April 2013 Mumps Outbreak in Guam
© 2013 Lippincott Williams & Wilkins www.pidj.com | 375
mumps cases to Guam DpHss. DpHss instituted active surveil-
lance april 20, 2010, at the peak of the outbreak with schools,
daycares, select provider clinics and laboratories reporting mumps
cases daily; close contacts of reported cases were investigated.
DpHss collected information on demographics, laboratory results,
symptom onset date, mumps-related complications and vaccina-
tion history. Vaccination status of all case-patients was verified by
healthcare providers; administration dates were noted.
Laboratory criteria for mumps diagnosis included isolation
of mumps virus from clinical specimens (ie, either an oropharyn-
geal or buccal mucosa swab), detection of mumps nucleic acid or
detection of mumps igM antibody measured by qualitative assays.
all culture, reverse transcription-polymerase chain reaction tests,18
mumps virus sequencing and genotype analysis19,20 were conducted
by the centers for Disease control and prevention (cDc). igM
tests were conducted at cDc and state and commercial labs.
the outbreak period was defined as December 1, 2009, to
December 31, 2010. We calculated mumps attack rates (aRs) for
the population overall and by sex, age and ethnicity. aR denomina-
tors were obtained from the projected 2010 Guam census data.15
Because census age groupings did not correlate with the age group
most affected by the outbreak, we created a 9-year to 14-year age
group category by adding one-fifth of the 5-year to 9-year census
age group to the 10-year to 14-year census age group.
Third Dose MMR Vaccine Intervention
public schools were eligible for the third dose intervention
if they had >90% 2-dose MMR vaccine coverage, ongoing mumps
transmission (ie, mumps cases in the preceding 2 weeks) and a
mumps aR of >5/1000. students in the intervention schools were
eligible if they were in the age group with the highest aR (aged 9−14
years), had a history of 2 MMR vaccine doses, had not previously
received a third MMR vaccine dose and had no history of mumps.
students who were not up-to-date with the recommended 2 doses
of MMR vaccine were offered appropriate vaccinations. school vac-
cination coverage was assessed by reviewing school vaccine records.
Vaccination status of students participating in the study was
confirmed either through immunization card review by parents or
immunization staff, or review of DpHss and school vaccine regis-
tries. For students with unknown or incomplete vaccination status,
verification was obtained from healthcare providers.
this study was approved by the cDc and Guam Memorial
Hospital institutional Review Boards. Written informed parental
consent and student assent were obtained.
Baseline and follow-up surveys captured demographic char-
acteristics, vaccination history, mumps history, clinical features and
complications of mumps, number of people in the household and
number of bedrooms in the house. Follow-up surveys also captured
possible adverse events after immunization. Baseline surveys were
distributed to all eligible students during the third dose MMR vac-
cine intervention from May 18 to May 21, 2010. Follow-up surveys
were distributed from october 4 to october 15, 2010, to the original
Mumps cases were identified by parental report on base-
line and follow-up surveys. to ensure completeness in ascertain-
ing cases, we supplemented our survey case count with confirmed
cases reported to Guam DpHss. if students were not reported as a
case to DpHss, did not report mumps in the baseline survey and
did not return a follow-up survey, they were categorized as non-
cases in our analysis.
Using the exact date of the vaccination clinic at the case-
students’ school, we compared mumps aRs after the intervention
between eligible students aged 9–14 years who received the third
MMR vaccine dose with nonrecipients (ie, students with documen-
tation of ≤2 doses of MMR vaccine) from postintervention day
22 through day 228 (ie, December 31, 2010, the end of the study
period). We excluded the 21 days (1 incubation period) after the
intervention from the analysis (May 22 to June 11, 2010) because
persons infected prior or during the intervention may have been
incubating mumps during this timeframe.1,21
all vaccine recipients were monitored 30 minutes postinter-
vention to evaluate immediate adverse events. the follow-up survey
contained questions on adverse events that may have occurred up
to 2 weeks postintervention, including any serious adverse events
resulting in permanent disability, hospitalization, life-threatening
illnesses or death.22
all data were analyzed with sas 9.2 (cary, nc). Denomi-
nators for school aRs were calculated using school enrollment
data. We compared postintervention mumps aRs between students
who received the third dose of MMR vaccine with those who did
not using Fisher's exact test. P values of <0.05 were considered sig-
nificant. Relative risks (RRs) and 95% confidence intervals (cis)
were calculated. crowding was assessed by dividing the number
of household members by bedrooms in the house. two-independ-
ent samples t tests were used to compare differences between the
means for household size and crowding between ethnic groups.
the first case of mumps was reported to DpHss on Febru-
ary 25, 2010, but the index case-patient was retrospectively identi-
fied as having parotitis onset December 7, 2009. the index case-
patient was a Guam resident who imported mumps from the island
of pohnpei where mumps was known to be circulating. Between
December 1, 2009, and December 31, 2010, 505 cases of mumps
were reported (Fig. 1) with a median age of 12 years (range: 2
months to 79 years; table 1); 50% were males. there were 5 (3.3%)
reports of orchitis among postpubertal males with 3 additional
reports of orchitis among prepubertal males aged 3, 7 and 9 years.
there were 2 hospitalizations for mumps-related illness; 1 was for
supportive care of orchitis and the other was misdiagnosed as neck
cellulitis but was later confirmed as mumps parotitis. no deaths
children aged 9–14 years had the highest overall aR
(8.4/1000), followed by those aged 5−8 years (5.3/1000), 15−19
years (3.9/1000) and 0−4 years (3.7/1000). adults 40 years and older
had the lowest aR (0.5/1000). correspondingly, all age groups <40
years were statistically more likely to have reported mumps case-
patients than adults 40 years or older, and children aged 9−14 years
had a 16 times higher risk (RR = 16.3, ci: 11.2–23.5). compared
to persons self-reporting “other” ethnicity, which comprised 32%
of the Guam population, persons who reported their ethnicity as
pohnpeian or chuukese had a markedly elevated risk of mumps
(pohnpeian [RR = 54.7, ci: 39.2−76.3] or chuukese [RR = 19.7,
ci: 14.5−26.9]). in contrast, persons reporting Filipino ethnicity did
not have an elevated risk and those reporting chamorro ethnicity
had a mildly elevated risk (table 1). ninety-six percent of mumps
case-patients aged 9–14 years were vaccinated with 2 doses of
MMR vaccine, followed by 90% of case-patients aged 5–8 years
and 88% of case-patients aged 15–19 years (table 2).
of 505 case-patients, 309 (61%) had sera tested for
mumps igM; 60 (19%) tested igM positive. twenty-eight (82%)
of 34 viral specimens tested positive by reverse transcription-
polymerase chain reaction, of which 14 (41%) also tested positive
by culture. (the difference in positive results between reverse
transcription-polymerase chain reaction and culture is likely
because 2 of the 3 shipments of specimens were not frozen on
Nelson et al The Pediatric Infectious Disease Journal • Volume 32, Number 4, April 2013
376 | www.pidj.com
© 2013 Lippincott Williams & Wilkins
arrival compromising specimen quality. in the only shipment
that arrived frozen, 11 of 14 specimens were positive by culture.)
sequence analysis of mumps viruses identified mumps genotype
G as the outbreak strain.
there are 64 public and private schools on Guam (preschool
through high school). seven (11%) schools (4 elementary and 3
middle schools) met the inclusion criteria with aRs ranging from
8.4 to 31.5/1000 among children aged 9−14 years (ie, grades 4−8).
these 7 schools were in the north and central regions of Guam, the
most densely populated part of the island. the high mumps aRs
of these 7 schools reflected the distribution of cases on Guam, as a
majority of the island’s case-patients occurred in this age group and
resided in the north and central regions. all 7 schools had 2-dose
MMR vaccine coverage between 99% and 100%.
MMR Vaccine Third Dose Intervention
the third dose intervention was implemented in the high-
est aR schools in the most affected age group (students aged
9–14 years), but occurred after the outbreak peaked (Fig. 2);
186 (37%) of the 505 outbreak cases occurred after the interven-
tion. there were 3364 students in grades 4−8 in the 7 selected
schools, of whom 3239 were eligible for the third dose inter-
vention. of those eligible, 1068 (33%) received a third dose of
MMR vaccine. at least 1 survey was returned by 2434 (75%)
eligible students, with 1236 (38%) returning a baseline and 2032
(63%) returning a follow-up survey. all 1068 vaccinees returned
a baseline survey and 734 (69%) returned a follow-up survey
(Fig. 3). nonrespondents were statistically more likely to be male
(P = 0.0024) and in grades 7−8 (P < 0.0001) compared with sur-
vey respondents. Despite differences between survey respondents
7 21 4 18 1 15 1 15 29 12 26 10 24 7 21 5 19 2 16 30 13 27 11 25 8 22 6 20 3
Dec.Jan.Feb.Mar. Apr.May Jun.Jul. Aug.Sept.Oct. Nov. Dec.
Number of cases
Follow-up survey administered
3rddose of MMR vaccine administered
FIGURE 1. Epidemiologic curve of reported mumps cases on Guam from December 1, 2009, to December 31, 2010. DPHSS,
Department of Public Health and Social Services.
TABLE 1. Demographic Characteristics of Mumps
Case-patients (n = 505) Compared With the Guam
General Population (n = 180,692), Guam, December 1,
2009, to December 31, 2010
(n = 505)
(n = 180,692)
Age group (yr)
TABLE 2. Vaccination Status by Age Group of Mumps
Case-patients, Guam, December 1, 2009, to December
The Pediatric Infectious Disease Journal • Volume 32, Number 4, April 2013 Mumps Outbreak in Guam
© 2013 Lippincott Williams & Wilkins www.pidj.com | 377
and nonrespondents, respondents reported similar demographic
characteristics proportionally compared with the Guam general
population with 1220 (50%) males, 1006 (41%) self-reporting
chamorro ethnicity and 1761 (77%) responding they had insur-
ance. students who received the third dose were statistically
more likely to be without health insurance (P = 0.008), female
(P < 0.0001) and in grades 4–6 (P = 0.0002), compared with
the mean household size among respondents was 6.2 mem-
bers (range: 2−26). chuukese respondents had the largest house-
hold size with a mean of 7.3 members (range: 2–26), followed by
pohnpeian respondents with a mean of 7.0 members (range: 2–17),
chamorro respondents with a mean of 6.2 members (range: 2–18)
and Filipino respondents with a mean of 5.7 members (ranges:
2–16). the mean number of household members among chuukese
and pohnpeian respondents was significantly higher than among
chamorro and Filipino respondents (P < 0.05).
the average crowding index among respondents was 2.3
persons per bedroom. pohnpeian and chuukese households had
the highest crowding indices with a mean of 3.1 and 3.0 persons
per bedroom (ranges: 1–10 and 1–13, respectively), compared with
chamorro and Filipino households which had crowding indices
of 2.2 and 2.1 persons per bedroom (ranges: 0.3–14 and 0.7–14,
respectively). the mean crowding index in pohnpeian and chu-
ukese households was significantly higher than in chamorro and
Filipino households (P < 0.0001).
six students eligible for the third MMR dose from 4 differ-
ent intervention schools were diagnosed with mumps in the postin-
tervention period; 5 (83%) did not receive the third MMR dose
and 1 (17%) received the third MMR dose (table 3). the student
with mumps who received the third dose of MMR vaccine was
igM negative and igG positive. the mumps aR was 2.6-fold lower
in those who received the third MMR dose compared with those
who did not (0.9/1000 versus 2.3/1000, RR = 0.4, ci: 0.05−3.5,
P = 0.67); this difference was not statistically significant (Fig. 4).
no immediate adverse events were reported. During the
2 weeks postvaccination, 32 (6.0%) students reported an adverse
event; the most frequent self-reported events were: joint aches
(2.6%), pain, redness and swelling at the injection site (2.4%) and
FIGURE 2. Mumps attack rates (cases/1000) by age group by 2-week period, Guam, December 1, 2009, to December 31, 2010.
FIGURE 3. Flow sheet of students eligible for participation
in the third dose MMR vaccine intervention and surveys,
Nelson et al The Pediatric Infectious Disease Journal • Volume 32, Number 4, April 2013
378 | www.pidj.com
© 2013 Lippincott Williams & Wilkins
dizziness (2.4%; table 4). no serious adverse events were reported,
and no medical attention was sought related to these events.
the Guam mumps outbreak was the third largest in the
United states and its territories since 2005, and the second outbreak
where a third dose of MMR vaccine was administered, thus provid-
ing an opportunity to evaluate the impact and safety of a third dose
MMR vaccine intervention in mumps outbreak control. although
the intervention occurred after the outbreak peaked, the aR in stu-
dents who received the third dose of MMR vaccine was 60% lower
than students with ≤2 doses during the postintervention period.
perhaps due to the smaller number of mumps cases that occurred
at this stage of the outbreak, the difference in aRs was not statisti-
cally significant. nonetheless, the effect of a third dose in boost-
ing immunity and increasing vaccine effectiveness is biologically
plausible; rapid anamnestic antibody responses after third MMR
vaccine doses have been reported.23
Mumps outbreaks have occurred in other populations with
high 2-dose vaccination coverage, including tradition-observant
orthodox Jewish adolescent school students,24 Midwestern college-
age students12 and international settings.25–27 some of the potential
contributors in those outbreaks, including high population density
and high contact rates, may also have contributed to the outbreak
in Guam. Guam families typically live in crowded environments
with large extended families (ie, Guam has a crowding index of
3.9 persons/household compared with 2.6 persons/household on
the Us mainland; survey respondents had an average of 6.2 family
members).15 Due to high contact rates among students, the impor-
tance of schools as high-risk transmission settings for mumps and
other outbreaks of vaccine-preventable diseases has been well doc-
compared with other 2-dose mumps outbreaks, some epi-
demiological features of this outbreak were unusual. children aged
9–14 years were disproportionately affected; this was a younger age
group than described in similar outbreaks.12,24 cases occurred in all
ethnic groups, but the highest aRs occurred in the ethnic minority
TABLE 3. Mumps Attack Rates Among Students Aged
9–14 Years in 7 Schools >1 Incubation Period After the
Third Dose MMR Vaccine Intervention, Guam 2010
More Than 1
Comparison of Attack
Rates Between Students
With 3 vs. ≤2
MMR Doses >1 Incubation
5 21712.3 Reference
1 1068 0.90.4 (0.05, 3.5)0.67
*Value calculated using Fisher's exact test.
Dec 3- Dec 10 Dec 11- Dec 24 Dec 25- Jan 7Jan 8- Jan 21
Jan 22- Feb 4Feb 5- Feb 18Feb 19- Mar 4 Mar 5- Mar 18 Mar 19- Apr 1 Apr 2- Apr 15Apr 16- Apr 29
Apr 30- May 13May 14- May 27 May 28- Jun 10Jun 11- Jun 24 Jun 25- Jul 8Jul 9- Jul 22 Jul 23- Aug 5
Aug 6- Aug 19
Aug 20- Sep 2
Sep 3- Sep 16
Sep 17- Sep 30Oct 1- Oct 14
Oct 15- Oct 28
Oct 29- Nov 11Nov 12- Nov 25
Nov 26- Dec 9
Dec 10- Dec 23
Dec 24- Jan 6
Eligible students aged 9-14 years in
7 interven?on schools
3rd dose MMR vaccine interven?on
Date of paro??s onset (2 week intervals)
Mumps a?ack rate (per 1000 persons)
AR 2.3/1,000 among ≤2-dose vaccinatedstudents*
AR 0.9/1000 among 3-dose vaccinatedstudents*
FIGURE 4. Comparison of mumps attack rates (cases/1000) postintervention among eligible students who received the third
MMR vaccine dose compared with those who did not receive the third dose, Guam, December 1, 2009, to December 31,
2010. *More than 1 incubation period postintervention.
The Pediatric Infectious Disease Journal • Volume 32, Number 4, April 2013 Mumps Outbreak in Guam
© 2013 Lippincott Williams & Wilkins www.pidj.com | 379
populations with the most household members and highest house-
hold crowding indices. We are unable to explain this epidemio-
logical finding but postulate that contributing factors may include
higher household density and/or genetic effects.
although this outbreak occurred in a highly vaccinated
population, there were lower transmission rates and fewer mumps-
related complications than would be expected in the absence of
appropriate vaccination. orchitis was reported among 3.3% of
postpubertal males. this is consistent with lower rates of com-
plications in fully vaccinated persons and with findings from the
northeast outbreak,13,24 but much less than prevaccine rates of 30%
(range 19%−44%) although the younger median age of postpuber-
tal cases in this outbreak should be considered when interpreting
this comparison.2,29–32 the occurrence of 3 reports of orchitis in
prepubertal males was unusual because there have only been 12
previously documented reports of prepubertal mumps orchitis.33,34
However, 2 of the 3 cases were reported by parents, and the third
patient was hospitalized for orchitis with no documented parotitis
or laboratory confirmation. previous studies have documented that
mumps can present as orchitis in the absence of parotitis.2,7
it was not surprising that only 19% of 309 cases showed
an igM response. case-patients who mount a secondary immune
response to mumps, as seen in most previously vaccinated per-
sons, may not have an igM response or it may be transient and not
detected depending on the timing of specimen collection.35 com-
mercial igM tests are less sensitive than mumps igM capture assays
(cDc unpublished data), and this also likely contributed to the low
rate of igM detection in this study.
Genotype G, the outbreak strain, was identified in the 2006
and 2009 to 2010 outbreaks in the United states, the outbreak in
canada in 2005 to 2006, the United Kingdom in 2004 to 2005
and is seen globally, although this lineage was different from the
northeast outbreak. Mumps is endemic throughout the world;
only 62% of countries vaccinate against mumps.36 it is possible
that since the last reported mumps outbreak on Guam in 1958 and
before this outbreak, mumps cases were imported on the island
from international visitors but went undetected; this may explain
why older children and adults were less affected. nonetheless,
although over 1 million international passengers visit Guam
annually,37 the index case-patient was a Guam resident who
traveled to another pacific island where mumps was known to be
MMR vaccine in the United states contains the Jeryl-Lynn
mumps strain.16,38 in postlicensure studies, vaccine effective-
ness against clinical mumps has a median effectiveness of 78%
(range: 49%–92%) for 1 dose of mumps vaccine and 88% (range:
66%−95%) for 2 doses of mumps vaccine.39–41 thus, although
reported mumps cases in the United states were 99% lower in
2010 compared with the prevaccine era, sustained transmission of
mumps in highly vaccinated 2 dose populations occurs in rare cir-
cumstances.12,24 We were unable to evaluate 2-dose vaccine effec-
tiveness during the outbreak in Guam due to the extremely high
2-dose coverage. effectiveness of 3 doses of mumps vaccine has
not been evaluated.
our findings are subject to limitations. Many families did
not visit a healthcare provider for subsequent ill family members,
likely leading to underreporting. there were anecdotal reports from
community leaders that there were large numbers of unreported
cases despite active surveillance. although transmission was still
occurring, the intervention occurred after the outbreak peaked. the
small numbers of mumps cases in the targeted population postin-
tervention limited our ability to draw firm conclusions about the
impact of the third dose intervention. there were statistically sig-
nificant differences between survey respondents and nonrespond-
ents, as well as among survey participants who received the third
dose of MMR vaccine and those who did not. However, these dif-
ferences are unlikely to bias the effect of a third dose of MMR vac-
cine. census data were not available to explore crowding indices by
ethnicity among the Guam general population.
implementing the third dose intervention in the school
setting allowed us to verify vaccination records while targeting
specific age groups in the most highly affected regions. However,
the third dose was only administered to 5.3% of all students aged
9–14 years making it difficult to draw conclusions about the
impact of the intervention at the population-level. More studies are
needed to find the optimal time to implement a third dose MMR
vaccine intervention. in the past 5 years in the United states, we
have experienced mumps outbreaks that have persisted for a couple
generations but have resolved without offering the third dose
intervention.42 However, the outbreak among the orthodox Jews
in the northeast and this outbreak persisted for months.14 With
delayed reporting in many outbreak contexts, it is often difficult to
ascertain when the peak of the outbreak is occurring, which makes
it challenging to know whether the outbreak will resolve on its own
or whether a third dose intervention is warranted.
Mumps outbreaks can cause a substantial economic and
resource burden on affected families and the public health sector,43
and targeted interventions may be a useful public health approach
in select high-risk transmission settings. the results of our study
suggest that the administration of a third dose of MMR vaccine may
be an effective method of controlling mumps outbreaks in 2-dose
vaccinated populations in specific settings. For future mumps out-
breaks in primarily 2-dose vaccinated populations, the focus should
be on ensuring that everyone is up-to-date with the recommended
2-dose vaccination schedule, as well as enforcing isolation meas-
ures and encouraging appropriate hygiene practices. our findings
support the need for additional evaluations that use third doses of
MMR vaccine for mumps outbreak control in highly 2-dose vac-
cinated populations and underscore the importance of initiating the
intervention early in the outbreak.
We would like to extend our thanks to Albert Barskey, Steph-
anie Bialek, Scott Grytdal, Mike Hudges, John McKenna, Carolyn
Parry, Rose Vibar, Gissela Villarruel, Jennifer Yara and the stu-
dents (Tina Cruz, Kristan Leon Guerrero, Noemi Ramirez and P. J.
Siquig) for their assistance during the field investigation. We would
like to thank all the outreach coordinators of the Department of
Education on Guam, Student Support Services Division, espe-
cially Doris Bukikosa, for their tireless efforts in helping us reach
TABLE 4. Self-reported Adverse Events During the 2
Weeks After the Third Dose MMR Vaccine Intervention
(N = 533)*, Guam 2010
Adverse Event Number (%)
Joint ache (n = 506)
Pain/redness (n = 509)
Dizzy (n = 509)
Fever (n = 512)
Syncope (n = 508)
Difficulty breathing (n = 509)
Hives/rash on the body (n = 508)
Sought medical care after third
dose of MMR vaccine (n = 487)
Any adverse event (n = 533)†
*Not all vaccinees completed this section of the survey.
†Eight respondents reported 2 adverse events, and 1 respondent reported 3 adverse
Nelson et al The Pediatric Infectious Disease Journal • Volume 32, Number 4, April 2013 Download full-text
380 | www.pidj.com
© 2013 Lippincott Williams & Wilkins
students during the follow-up survey. We also extend our thanks to
Robert Haddock for his historical knowledge of mumps outbreaks
on Guam. Finally, we would like to thank the public health nursing
staff, especially Margarita Gay, for helping us with the school vac-
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