Does restricted distribution limit access and coverage of yellow fever vaccine in the United States?

Yellow fever, the original “viral hemorrhagic fever,” is a mosquito-borne infection characterized by hepatic, renal, and myocardial injury, bleeding, and a high case-fatality rate. The disease occurs in tropical South America and sub-Saharan Africa. Maintained by zoonotic transmission between sylvan mosquitoes and nonhuman primates, the virus cannot be eradicated, and prevention of human infection requires high vaccination coverage. Recently the incidence of yellow fever has increased dramatically (1), with 23,543 cases and 6,421 deaths officially reported to the World Health Organization (WHO) between 1985 and 1996. The true incidence is believed to far exceed the reported incidence. Yellow fever remains a public health problem because of failure to implement effective immunization, particularly in Africa. The recent upsurge in yellow fever activity has been associated with an increased risk for infection among unimmunized travelers. In 1996, two tourists infected in the Amazon region of Brazil died after returning to the United States (2) and Switzerland (3). Fatal and other cases in tourists were also reported in previous years (4-8). Other cases were likely missed, misdiagnosed as viral hepatitis, treated abroad, or not reported. Since viremic humans are the source of infection for the epidemic mosquito vector Aedes aegypti, unimmunized travelers may import yellow fever to Ae. aegypti-infested regions, including the United States, West Indies, Central America, Mediterranean region, and Asia. The expansion of international travel, including adventure travel to remote and tropical areas, has increased exposure to yellow fever and other exotic infections (9). Each year eight to nine million tourists arrive in yellow fever-endemic countries in South America and Africa (10,11); the number of tourists visiting regions within countries in which yellow fever transmission occurs is unknown but probably exceeds three million. In the United States, 150,000 to 300,000 civilian travelers are immunized annually (12)—likely only a fraction of the population requiring the vaccine. However, few data exist on vaccine coverage in travelers to yellow fever–endemic regions. One survey in the United States found that 30% of travelers to developing countries between 1980 and 1986 received yellow fever vaccine (13). Yellow fever vaccine coverage of European travelers varied from 0% to 90% (14,15). WHO and the Centers for Disease Control and Prevention strongly recommend vaccination for travel outside urban areas in the yellow fever–endemic zone (16,17). Yellow fever 17D, a live, attenuated, vaccine developed in 1936, has been used in more than 300 million persons and has a remarkable record …