International Importations of Measles Virus into the United States during the Post-Elimination Era, 2001–2015

Abstract

BackgroundMeasles is a highly contagious vaccine-preventable disease that can lead to serious complications. Although measles was declared eliminated from the United States in 2000, measles cases and outbreaks continue to occur each year as a result of importations of the disease from countries in which it remains endemic. We describe the epidemiology of importations of measles virus into the US during the post-elimination era.MethodsMeasles is nationally notifiable in the USA and local and state health departments report confirmed measles cases to the Centers for Disease Control and Prevention (CDC). A case is considered internationally imported if at least some of the exposure period (7-21 days before rash onset) occurred outside of the USA, rash onset occurred within 21 days of entering the USA, and there was no known exposure to measles in the US during that time. We describe the demographic characteristics, source regions, and vaccination status of measles importations during 2001–2015.ResultsFrom 2001 to 2015, 2,012 measles cases were reported to CDC; 535 (27%) were imported. A median of 28 importations occurred each year (range: 18–80). The median age of imported cases was 18 years (range: <1–75 years), 50% were male, 87% were unvaccinated or had unknown vaccination status, and 63% reported travel to countries in the Western Pacific and European Regions of the World Health Organization during their exposure periods. Half of all imported cases had rash onset between January and April. Overall, 62% (n = 332) of importations occurred among US residents, varying from a low of 37% in 2001 to a high of 89% in 2014. One imported case occurred among a US resident too young to be vaccinated, and 15 (5%) occurred among US residents born before 1957 (presumed immune from natural disease), and thus were not vaccine preventable.ConclusionImportations of measles virus will continue to occur as long as measles remains endemic in many parts of the world. In the post-elimination era in the US, the majority of importations were among US residents, almost all of which were vaccine preventable. Our findings emphasize the importance of measles vaccination of individuals aged ≥6 months prior to international travel, per ACIP recommendations, and of supporting global measles control efforts.Disclosures All authors: No reported disclosures.