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What’s Behind the Latest Measles Outbreaks?

Concerns about a possible link between the measles, mumps and rubella, or MMR, vaccine helped fuel a measles outbreak this year in Minnesota, the country’s largest since 1996, according to research to be presented Saturday at an infectious diseases meeting.

Oct. 20, 2011 -- Safety concerns about the measles, mumps, and rubella (MMR) vaccine helped fuel a measles outbreak this year in Minnesota. It was the country’s largest measles outbreak since 1996.

Research on the outbreak is slated to be presented Saturday at an infectious diseases meeting.

From January to July, 174 cases of measles were reported in the U.S. In Minnesota, 26 people contracted measles from February through April, says Pam Gahr, MPH, an epidemiologist with the Minnesota Department of Health. Patients ranged in age from 4 months to 51 years, and all of the cases occurred in two counties in metropolitan Minneapolis-St. Paul.

“Quite a few of the children were not old enough to be vaccinated,” she says. “That we can’t do much about. There are always going to be susceptible babies.”

Sixteen of the children were hospitalized, but all recovered. In each of the affected counties, Gahr says, the outbreak was started by an unvaccinated child who became infected while in Kenya, where it’s endemic.

Of the 26 cases, eight were Somalis, Gahr says. Minnesota has the largest Somali population in the United States, estimated to number 25,000 to 40,000.

Somalis’ Low Immunization Rates

Immunization rates are far lower in Somali children than in non-Somali children, according to research Gahr and her co-authors will present at the Infectious Diseases Society of America meeting in Boston. Among children in Hennepin County, in which Minneapolis is located, only 57% of Somali children born in 2009 had received the first of the recommended two MMR doses, compared to 85% of other children.

“The Somali community is particularly concerned about the safety of MMR and its perceived association with autism,” Gahr says. “Because there’s not a real clear explanation for what causes autism, people grasp for something concrete.”

In the past year, Andrew Wakefield, the British researcher whose 1998 paper, now discredited, popularized the idea that the MMR vaccine causes autism, met at least twice with Somali parents in Minnesota, according to news reports.

A recent study of children in the Minneapolis early childhood special education program suggested autism might be more common in Somali children, heightening parents’ concerns, says Lynn Bahta, RN, PHN, a consultant for the state health department’s immunization program. “The community really took that to heart,” Bahta says, even though researchers couldn’t confirm the children’s autism diagnosis because they didn’t have access to their medical records.

The measles outbreak did spur parents to immunize unvaccinated children because it made them see the disease as a real threat, she says.

But infectious disease specialist Paul Offit, MD, director of the Vaccine Information Center at the Children’s Hospital of Philadelphia, says “once you’ve introduced the notion that something is possibly a problem ... it’s hard to un-ring the bell.”

Quebec’s Measles Outbreak

The largest measles outbreak in North America this year has been in the Canadian province of Quebec, where 757 cases were confirmed as of Oct. 5. A quarter of the cases were in people who had written proof that they’d received both doses of the MMR vaccine, while an additional 10% reported being immunized, says Gaston de Serres, MD, PhD, a medical epidemiologist at the Quebec Institute of Public Health and co-author of two studies about the Quebec outbreak that will be presented at the infectious diseases meeting.

De Serres will report on 100 cases that occurred in a single high school. At that school, half of the students who came down with the measles had been fully immunized against the disease.

He says he suspects that has to do with the fact that Canadian doctors recommend getting the first dose at 12 months, while U.S. doctors give parents a grace period of 12 to 15 months. The vaccine contains live measles virus, and at 12 months, babies may still have measles antibodies from their mothers that would attack the virus, lessening the vaccine’s effectiveness.

Plus, Canadian doctors recommend administering the second dose at 18 months, while U.S. doctors advise waiting until children are about to enter kindergarten, at about age 4 or 5.

However, de Serres says, he’d be uneasy saying the Canadian policy should change on the basis of his findings alone.

These studies will be presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.

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