Where Measles Can Thrive

Past measles outbreak reveals dangers of low vaccination rates

(RxWiki News) Measles cases are the highest they have been since 2000, exceeding the previous high in 2011. Like this year's, the 2011 outbreaks resulted from low vaccination coverage.

A recent study looked more closely at one of the outbreaks in 2011 that occurred in Minnesota. That outbreak primarily occurred within a Somali community that had previously had high vaccination rates.

However, by the time the outbreak occurred, the vaccination coverage in the community had been cut nearly in half.

This low rate of vaccination, partly a result of unfounded safety concerns, appeared to play a role in the size of the outbreak.

"Discuss vaccinations with your child's pediatrician."

The study, led by Pamala Gahr, MPH, of the Minnesota Department of Health in St. Paul, Minnesota,

When a child was found to have measles in Minnesota in March, 2011, public health officials sought to determine how the child had caught the disease.

The child had not traveled overseas, which was the usual way that the disease had been introduced to the US since 2000, when measles was declared eliminated from the US.

A measles outbreak ensued, and public health officials worked to prevent the disease from spreading and understand how it was affecting the community.

Overall, 21 individuals became sick with the measles, half of whom were less than 1 year old, when the measles vaccine (MMR) is typically given.

The ages of those who became ill with measles ranged from 4 months old to 51 years old, and two thirds of those who became sick (14 cases) needed to be hospitalized for two to seven days.

Eventually public health officials identified the source of the measles: A 2-year-old child who had been born in the US but visited Kenya had returned to the US with the disease.

During the course of the entire outbreak, 3,000 people were exposed to the disease.

Among the 21 measles cases, 16 of the individuals had not been vaccinated even though nine of them were old enough to be vaccinated.

Of the nine who had been old enough to be vaccinated but were not, seven were not vaccinated because of safety concerns about the vaccine.

Evidence about the measles-mumps-rubella (MMR) vaccine have found it to be safe and effective and to have extremely low risks of negative side effects.

Yet vaccine coverage within the Somali community where the outbreak was centered dropped steeply between 2004, when it was 91 percent, and 2010, when it was at 54 percent.

"This was the largest measles outbreak in Minnesota in 20 years, and aggressive response likely prevented additional transmission," the researchers wrote.

"Measles outbreaks can occur if under-vaccinated subpopulations exist," they wrote. "Misunderstandings about vaccine safety must be effectively addressed."

The study was published June 9 in the journal Pediatrics. The research was funded by the US Centers for Disease Control and Prevention. The authors reported no conflicts of interest.

Review Date: 
June 8, 2014