What is causing an increase in the incidence of measles in the US?

Updated: Jun 06, 2019
  • Author: Selina SP Chen, MD, MPH; Chief Editor: Russell W Steele, MD  more...
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Answer

Although the elimination of endemic measles transmission in the US in 2000 was sustained through at least 2011, according to a CDC study, cases continue to be caused by virus brought into the country by travelers from abroad, with spread occurring largely among unvaccinated individuals. In 88% of the cases reported between 2000 and 2011, the virus originated from a country outside the US, and 2 out of every 3 individuals who developed measles were unvaccinated. Moreover, the director of the CDC noted that, in 2013, US measles cases increased threefold from the previous median, to 175 cases. [1, 2] Most of these cases were outbreaks in children whose parents had refused immunization.

This trend of increased incidence continued into 2014. From January 1 to May 23, 2014, 288 confirmed cases were reported to the CDC, a figure that exceeds the highest reported annual total number of cases (220 cases in 2011) since measles was declared eliminated in the United States in 2000. Of the 288 cases, 200 (69%) occurred in unvaccinated individuals and 58 (20%) in persons with unknown vaccination status. Nearly all of the 2014 cases reported thus far (280 [97%]) were associated with importations from at least 18 countries. Eighteen states and New York City reported measles infections during this period, and 15 outbreaks accounted for 79% of reported cases, including a large ongoing outbreak in Ohio primarily among unvaccinated Amish persons, with 138 cases reported. [3]


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