International importations of measles virus into the United States during the postelimination era, 2001-2016

Abstract

Background: Although measles was declared eliminated from the United States in 2000, measles cases and outbreaks continue to occur, resulting from importations of the disease from countries where it remains endemic. Methods: We describe the epidemiology of international importations of measles virus into the United States during the postelimination era. Results: From 2001 to 2016, 553 imported measles cases were reported to the Centers for Disease Control and Prevention. A median of 28 importations occurred each year (range: 18-80). The median age of imported case-patients was 18 years (range: 3 months-75 years); 87% were unvaccinated or had an unknown vaccination status. US residents (as opposed to foreign visitors) accounted for 62% of imported measles cases. Overall, 62% of all imported case-patients reported travel to countries in the Western Pacific and European Regions of the World Health Organization during their exposure periods. The number of measles importations from specific countries was related to the incidence of measles in and the volume of travel to and from the source country. Conclusions: Our findings emphasize the importance of measles vaccination of US residents aged 6 months before international travel according to the Advisory Committee on Immunization Practices recommendations and supporting global measles elimination efforts.