Measles Transmission Continues in Minnesota

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Low measles-mumps-rubella (MMR) vaccination coverage in a Minnesota community led to an outbreak and rapid spread of measles in April and May of this year, US officials report. The outbreak resulted in 20 hospitalizations and thousands of exposures in child care centers, schools, and healthcare facilities.

In early April, measles of the same genotype (B3) was confirmed in three children with no record of MMR vaccination who attended the same daycare facility in Hennepin County, Minnesota. By May 31, 2017, a total of 65 confirmed measles cases across four counties (Hennepin, Ramsey, LeSueur, and Crow Wing) had been reported to the Minnesota Department of Health, and transmission is ongoing, researchers from the Centers for Disease Control and Prevention report in the July 13 issue of the Morbidity and Mortality Weekly Report.

Indigenous measles transmission has been eliminated in the United States, but the virus, which continues to circulate in other areas of the world, is often introduced into the United States by international travellers. “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,” the authors hypothesize.

Of the 65 identified cases, nearly all (95%) occurred in unvaccinated patients, on the basis of vaccination status verified through the Minnesota Immunization Information Connection, and 85% occurred in US-born children of Somali descent. Approximately one third of the patients were hospitalized for treatment of dehydration or pneumonia.

Of the unvaccinated patients who developed measles, 50 (77%) were children aged 12 months or older who were eligible for vaccination because of their age.

Between April 10, when the Minnesota Department of Health received notification of the first suspected measles case, and May 31, the virus was confirmed in patients from five schools, 12 child care centers, three healthcare facilities, and multiple households. In total, according to the report, “an estimated 8,250 persons were potentially exposed to measles in these settings.”

Since 2008, there has been a precipitous drop in MMR vaccination coverage among Minnesota-born Somali children. “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,” the authors write. “The low vaccination rate resulted in a community highly susceptible to measles.”

Before 2008, the 1-dose MMR vaccination coverage rate among Somali children aged 2 years in Hennepin County was higher than 90%. In 2011, a smaller measles outbreak (21 cases, including eight in Somali children) occurred. At that time, the vaccination coverage rate had dropped to 54%, despite the development of culturally appropriate educational initiatives designed to build trust in the Somali community and combat misinformation about the vaccine, the authors write. By 2014, the coverage rate had dropped to 35.6%.

With the current outbreak, the Minnesota Department of Health has increased its outreach efforts, including education, increased postexposure prophylaxis, and recommendation of an accelerated MMR schedule for all children living in Hennepin County and for all Minnesota Somali children regardless of county of residence. Specifically, the authors write, “to provide additional protection, a second dose of MMR vaccine was recommended for children who had received a first dose >28 days previously.”

According to data from the Minnesota Immunization Information Connection, the average number of MMR vaccine doses administered per week in Minnesota had increased by mid-May from 2700 doses before the outbreak to 9964, the authors write.

“High measles vaccination coverage rates across subpopulations within communities are necessary to prevent the spread of measles,” the authors stress. “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.”

The authors have disclosed no relevant financial relationships.

Morb Mortal Wkly Rep. 2017;66:713-717. Full text

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