On April 10, 2017, the Minnesota Department of Health (MDH) was notified about a suspected
measles case. The patient was a hospitalized child aged 25 months who was evaluated
for fever and rash, with onset on April 8. The child had no history of receipt of
measles-mumps-rubella (MMR) vaccine and no travel history or known exposure to measles.
On April 11, MDH received a report of a second hospitalized, unvaccinated child, aged
34 months, with an acute febrile rash illness with onset on April 10. The second patient’s
sibling, aged 19 months, who had also not received MMR vaccine, had similar symptoms,
with rash onset on March 30. Real-time reverse transcription–polymerase chain reaction
(rRT-PCR) testing of nasopharyngeal swab or throat specimens performed at MDH confirmed
measles in the first two patients on April 11, and in the third patient on April 13;
subsequent genotyping identified genotype B3 virus in all three patients, who attended
the same child care center. MDH instituted outbreak investigation and response activities
in collaboration with local health departments, health care facilities, child care
facilities, and schools in affected settings. Because the outbreak occurred in a community
with low MMR vaccination coverage, measles spread rapidly, resulting in thousands
of exposures in child care centers, schools, and health care facilities. By May 31,
2017, a total of 65 confirmed measles cases had been reported to MDH (Figure 1); transmission
is ongoing.
FIGURE 1
Number of measles cases (N = 65) by date of rash onset — Minnesota, March 30–May 27,
2017
The figure above is a histogram, an epidemiologic curve showing the 65 measles cases
by date of rash onset in an outbreak in Minnesota during March 30–May 27, 2017.
Investigation and Results
After receiving notification of the first case on April 10, MDH and the Hennepin County
Human Services and Public Health Department began an investigation. The Council of
State and Territorial Epidemiologists and CDC case definition* was used to identify
confirmed cases of measles in Minnesota (
1
). A health alert was issued April 12, which notified health care providers of the
two measles cases in Hennepin County and provided recommendations concerning laboratory
testing for measles and strategies to minimize transmission in health care settings.
Emphasis was placed on recommendations for all children aged ≥12 months to receive
a first dose of MMR. Providers identified patients with suspected measles based on
clinical findings and reported suspected cases to MDH. Testing with rRT-PCR was performed
at MDH on nasopharyngeal or throat swabs and urine specimens. Among persons testing
positive by rRT-PCR who had received vaccine ≤21 days before the test, genotyping
was performed to distinguish wild-type measles virus (genotype B3 virus) from the
vaccine virus (genotype A virus). Patients (or their parents or guardians) with confirmed
measles were interviewed by local public health officials to confirm symptoms, onset
date, and exposure history for the 21 days before rash onset and identify contacts
during their infectious period (4 days before through 4 days after rash onset). Contacts
were defined as persons who had any contact with patients during their infectious
period.
Among the 65 confirmed cases, the median patient age was 21 months (range = 3 months–49
years). Patients were residents of Hennepin, Ramsey, LeSueur, and Crow Wing counties.
During April 10–May 31, confirmed measles patients were identified in five schools,
12 child care centers, three health care facilities, and numerous households; an estimated
8,250 persons were potentially exposed to measles in these settings. Rash onset dates
ranged from March 30–May 27, 2017. Sixty-two (95%) cases were identified in unvaccinated
persons, including 50 (77%) in children aged ≥12 months (i.e., age-eligible for MMR
vaccination). U.S.-born children of Somali descent (Somali children) accounted for
55 (85%) of the cases. Among the three patients with a history of measles vaccination,
all had received 2 MMR doses before illness onset. As of May 31, 20 (31%) patients
had been hospitalized, primarily for treatment of dehydration or pneumonia; no deaths
had been reported.
Public Health Response
Rosters and attendance records were obtained from child care centers and schools where
persons might have been exposed to measles, and the vaccination status of each attendee
was verified through the Minnesota Immunization Information Connection, a system that
stores electronic immunization records (http://www.health.state.mn.us/miic). Health
care facilities similarly identified contacts who were exposed to measles patients
and followed up with susceptible (i.e., unvaccinated, pregnant, or immunocompromised)
exposed persons. In accordance with the Advisory Committee on Immunization Practices
2013 guidelines (
2
), postexposure prophylaxis (PEP) with MMR or immune globulin was recommended for
susceptible, exposed persons. Persons who received PEP with MMR within 72 hours of
exposure or with immune globulin within 6 days of exposure were placed on a 21-day
self-monitoring symptom watch for development of fever or rash, but could continue
attending child care and school. Susceptible exposed persons who did not receive PEP
according to recommendations were excluded from child care centers or school, and
MDH recommended that they avoid public gatherings for 21 days, including having visitors
who were susceptible to measles virus. By May 31, at least 154 persons had received
PEP (26 MMR doses and 128 courses of immune globulin), and 586 susceptible exposed
persons who did not receive recommended PEP were excluded from child care centers
or school and advised to receive MMR vaccination to protect against future measles
illness.
On April 18, as the outbreak continued, MDH recommended an accelerated MMR schedule;
to provide additional protection, a second dose of MMR vaccine was recommended for
children who had received a first dose >28 days previously.
†
These recommendations were initially for all children living in Hennepin County and
for all Minnesota Somali children regardless of county of residence, because MMR coverage
rates among Somali children in Hennepin County have declined since 2007. In 2014,
coverage with the first dose of MMR among Somali children in Hennepin County was 35.6%
(Figure 2). In response to the rapid increase in the number of reported cases, on
May 4, 2017, MDH recommended an accelerated vaccination schedule for all children
aged ≥12 months residing in all counties where a measles case had been reported during
the previous 42 days; MDH further recommended that health care providers throughout
the state consider using an accelerated schedule.
FIGURE 2
Percentage of children receiving measles-mumps-rubella vaccine at age 24 months among
children of Somali and non-Somali descent, by birth year — Hennepin County, Minnesota,
2004–2014
Source: Minnesota Immunization Information Connection, Minnesota Department of Health.
The figure above is a line graph showing the percentages of Somali and non-Somali
children who received measles-mumps-rubella vaccine at age 24 months, by birth year,
in Hennepin County, Minnesota, during 2004–2014.
Previously established culturally appropriate community outreach approaches (e.g.,
working with community and spiritual leaders, interpreters, health care providers,
and community members) (
3
) were intensified during the outbreak. Using existing partnerships, state and local
public health officials worked with MDH Somali public health advisors, Somali medical
professionals, faith leaders, elected officials, and other community leaders to disseminate
educational materials, attend community events, and create opportunities for open
dialogue and education about measles and concerns about MMR vaccine. Child care centers
and schools were provided talking points and informational sheets on measles and MMR
vaccine, and posters with key messages were distributed in mosques and shopping malls
popular with the Somali community. Community outreach focused on oral communication,
which is preferred by this community, including radio and television messaging and
telephone call-in lines that permit approximately 500 persons at a time to listen
to a health professional.
Outreach to encourage vaccination was increased during the outbreak. By the second
week of May, the average number of MMR vaccine doses administered per week in Minnesota
had increased from 2,700 doses before the outbreak to 9,964, as reported by the Minnesota
Immunization Information Connection.
Discussion
Minnesota law requires that children aged ≥2 months be vaccinated against certain
diseases or file a medical or conscientious exemption to enroll in school, child care,
or school-based early childhood programs. Before 2008, first-dose MMR vaccination
coverage among Minnesota-born Somali children aged 2 years in Hennepin County exceeded
90%. However, MMR vaccination coverage rates declined among Minnesota’s Somali-American
community members starting with the 2008 birth-year cohort. The decline in vaccination
coverage was in response to concerns about autism, the perceived increased rates of
autism in the Somali-American community, and the misunderstanding that autism was
related to MMR vaccine (3,4). Studies have consistently documented that there is not
a relationship between vaccines and autism (5,6). The low vaccination rate resulted
in a community highly susceptible to measles. Parental concerns were addressed by
building trust with the community and identifying effective, culturally appropriate
ways to address questions, concerns, and misinformation about MMR vaccine. In 2011,
a smaller measles outbreak began in the Somali community in Hennepin County and resulted
in 21 cases, including eight cases in persons of Somali descent (
4
,
7
). At that time, the 1-dose MMR vaccination coverage rate among Somali children aged
2 years in Hennepin County was 54%. The source of the 2011 outbreak was a Somali child
aged 30 months who acquired measles while visiting Kenya (
7
). However, the source of the current outbreak is unknown, which suggests that additional
cases have likely occurred that did not come to the attention of health care providers
or public health departments.
Although indigenous measles transmission has been eliminated in the United States,
the virus continues to circulate widely in many regions of the world, including Africa,
Europe, and parts of Asia, and is often introduced into the United States by international
travelers (
8
). High measles vaccination coverage rates across subpopulations within communities
are necessary to prevent the spread of measles. The current Minnesota measles outbreak,
with 31% (20 of 65) of cases requiring hospitalization, demonstrates the importance
of addressing low vaccination coverage rates to ensure that children are adequately
protected from a potentially serious vaccine-preventable disease (
3
).
Summary
What is already known about this topic?
Measles was declared eliminated from the United States in 2000 but continues to circulate
in many regions of the world and can be imported into the United States by travelers.
Measles vaccine is highly effective, with 1 dose being 93% effective and 2 doses being
97% effective at preventing measles.
What is added by this report?
In a community with previously high vaccination coverage, concerns about autism, the
perceived increased rates of autism in the Somali-American community, and the misunderstanding
that autism was related to the measles-mumps-rubella (MMR) vaccine resulted in a decline
in MMR vaccination coverage to a level low enough to sustain widespread measles transmission
in the Somali-American community following introduction of the virus. Studies have
consistently documented that there is not a relationship between vaccines and autism.
What are the implications for public health practice?
This outbreak demonstrates the challenge of combating misinformation about MMR vaccine
and the importance of creating long-term, trusted relationships with communities to
disseminate scientific information in a culturally appropriate and effective manner.