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On March 16, 2018, this report was posted as an MMWR Early Release on the MMWR website (https://www.cdc.gov/mmwr).
Yellow fever virus is a mosquito-borne flavivirus that causes yellow fever, an acute infectious disease that occurs in South America and sub-Saharan Africa. Most patients with yellow fever are asymptomatic, but among the 15% who develop severe illness, the case fatality rate is 20%-60%. Effective live-attenuated virus vaccines are available that protect against yellow fever (1). An outbreak of yellow fever began in Brazil in December 2016; since July 2017, cases in both humans and nonhuman primates have been reported from the states of Sao Paulo, Minas Cerais, and Rio de Janeiro, including cases occurring near large urban centers in these states (2). On January 16, 2018, the World Health Organization updated yellow fever vaccination recommendations for Brazil to include all persons traveling to or living in Espirito Santo, Sao Paulo, and Rio de Janeiro states, and certain cities in Bahia state, in addition to areas where vaccination had been recommended before the recent outbreak (3). Since January 2018, 10 travel-related cases of yellow fever, including four deaths, have been reported in international travelers returning from Brazil. None of the 10 travelers had received yellow fever vaccination.
Five of the 10 cases were reported by ProMED since January 15, including two from Argentina and three from Chile; two of the travelers from Chile died. In addition, during January 1-March 15, 2018, five confirmed cases of yellow fever in unvaccinated travelers returning from Brazil were reported by GeoSentinel (http://www.istm.org/geosentinel), the global clinician-based sentinel surveillance system for travel-related illness among international travelers and migrants (4). These five yellow fever cases...