Largest Measles Outbreak in Years Tells Cautionary Tale, Underscores Importance of Vaccination

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This year’s jump in measles in the United States and Canada was costly and occurred among unvaccinated children and adults, suggest several studies being presented at the 49th annual meeting of the Infectious Diseases Society of America (IDSA).

Thanks to a successful infant measles, mumps and rubella (MMR) vaccination program, measles has been declared eliminated in the United States – meaning the illness hasn’t had continuous spread – since 2000. But outbreaks can occur when the infection is imported, typically by unvaccinated Americans who are infected while traveling to Europe or other continents and then return home, or by foreign tourists who are infected and travel to this country.

Measles is very contagious and can spread quickly in communities with low vaccination rates and among those who are not fully vaccinated (including infants and other vulnerable populations). This is the largest number of reported measles cases in many years: 15 years in the United States and 16 years in Canada.

“Forest fires start with sparks, but unless there is sufficient dry tinder, they won’t roar out of control,” says James M. Hughes, MD, IDSA president. “The same is true of outbreaks. The occasional case is not an issue, but when it occurs in a community where a fair number of people are not vaccinated it can cause serious problems. This is why vaccination is important. We don’t want to return to the days when measles and other vaccination-preventable diseases were rampant.”

Before measles vaccination was available in the 1960s, in the United States every year about three to four million people were infected with measles, 48,000 were hospitalized, 1,000 were permanently disabled and about 500 died, according to the Centers for Disease Control and Prevention (CDC).

U. S. Measles Outbreak Largest Since 1996

In 2011 to date, 212 people with measles have been reported in the United States, 68 were hospitalized and at least 12 of them had pneumonia, reports the CDC. This is the largest number of measles cases since 1996. Rapid public health response efforts prevented measles cases and outbreaks from becoming much larger, by isolating cases and vaccinating those who were unvaccinated.

Of those infected, 183 (86 percent) were unvaccinated, or their vaccination status was unknown and 27 (13 percent) were less than a year old. Most of the imported measles cases occurred among U.S. residents traveling overseas to Western Europe (47 percent), Africa or Asia, where vaccination rates are significantly lower, and measles is an ongoing problem.

“The MMR vaccine is very safe and effective at preventing measles, and high coverage is critical for preventing outbreaks,” says Huong McLean, PhD, epidemiologist at the CDC. “Quick public health response limited the spread of the disease. But the more unvaccinated people there are in a community, the more difficult it is to control an outbreak.”

Controlling Measles Outbreaks Costly

An outbreak of measles in spring 2011 in Salt Lake County, Utah, began when an unvaccinated local high school student returned home after traveling in Europe, where he was infected. Rapid response to control the outbreak limited it to nine people in Salt Lake County, yet managing the outbreak cost approximately 300,000 for infection control measures by two local hospitals and the local and state health departments. That cost includes physician and staff time, vaccines, immunoglobulin and blood tests, reports the Utah Department of Health.

When a child or adult with measles goes to school, everyone in the school is exposed, and Utah state law dictates that unvaccinated children and teachers (including those who cannot locate their vaccination records) must stay home for 21 days after the exposure. To contain the outbreak, 12,000 people were contacted about possible exposure and 184 people were quarantined, including 51 students. Costs to the schools associated with these actions – such as the hiring of substitute teachers and state money that is withheld from the schools when kids stay home – were not factored into the study.

Six of those infected (67 percent) were not vaccinated due to personal exemptions, including the student initially infected. Personal exemptions include philosophical or any other unspecified non-medical exemption.

“It is always a concern to have a large number of unvaccinated people in close proximity,” said Karyn Leniek, MD, MPH, deputy state epidemiologist for the Utah Department of Health. “Our goal is to have as many people vaccinated as possible to protect those who cannot receive the vaccine and who are not fully immunized.”

Vulnerable Population Center of Minnesota Outbreak

The largest U.S. measles outbreak began in March with a 2-1/2 year old unvaccinated child who had recently traveled to Kenya and who attended a drop-in childcare center. Overall, 21 people were infected, and 14 (67 percent) were hospitalized. Among those who became ill were nine people living in homeless shelters.

The outbreak was sustained in part due to a low rate of vaccination among children of Somali descent: state immunization registry data for Hennepin County, Minn. Show a gap between MMR vaccination rates of Somali children and non-Somali children. Equally important was transmission in shelters where children had missed vaccination opportunities, and congregate living made public health interventions such as isolation and quarantine challenging. None of the measles cases who were of Somali descent were shelter residents. However, there was transmission to the shelter community through a drop-in child care center that both non-shelter and shelter residents attend.

“Healthcare providers together with public health and community leaders must address growing vaccine hesitancy to ensure high immunization rates in all communities,” says Pam Gahr, MPH, senior epidemiologist with the Minnesota Department of Health, St. Paul.

Large Quebec Outbreak Sustained by the Unvaccinated

Quebec, Canada is experiencing its largest measles outbreak since 1989, with 757 confirmed cases as of Oct. 5. The outbreak appears to have been imported: 18 people acquired measles while traveling outside of the country (17 in Europe). Of those infected: 505 (67 percent) had not been vaccinated or their vaccination status was unknown and 70 (10 percent) received only one dose); 467 (62 percent) were 10-19 years old; 88 (12 percent) were hospitalized and this proportion was higher among adults older than 30 (25 percent) and children ages 12 to 17 months old (22 percent).

“This outbreak is being fed largely on unvaccinated or undervaccinated people, but we were concerned that a significant number had received the recommended two doses of MMR vaccine,” says Philippe Belanger, MSc, epidemiologist at Ministère de la Santé et des Services Sociaux du Quebec, Montreal.

“These outbreaks provide some insight into what can happen when people don’t get vaccinated and therefore aren’t protected against these preventable diseases,” says Hughes. “Not only do they get sick, but they put infants and other vulnerable groups at risk.”

 

 

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