Abstract
Due to the risk of severe vaccine-associated adverse events, yellow fever vaccination in Brazil is only recommended in areas considered at risk for disease. From September 2008 through June 2009, two outbreaks of yellow fever in previously unvaccinated populations resulted in 21 confirmed cases with 9 deaths (case-fatality, 43%) in the southern state of Rio Grande do Sul and 28 cases with 11 deaths (39%) in Sao Paulo state. Epizootic deaths of non-human primates were reported before and during the outbreak. Over 5.5 million doses of yellow fever vaccine were administered in the two most affected states. Vaccine-associated adverse events were associated with six deaths due to acute viscerotropic disease (0.8 deaths per million doses administered) and 45 cases of acute neurotropic disease (5.6 per million doses administered). Yellow fever vaccine recommendations were revised to include areas in Brazil previously not considered at risk for yellow fever.
Highlights
Yellow fever is an acute viral hemorrhagic disease transmitted by mosquitoes
Yellow fever is a viral hemorrhagic disease transmitted by mosquitos, endemic in tropical regions of Africa and South America
Large urban outbreaks of yellow fever have been eliminated in the Americas, where most yellow fever cases result from human exposure to jungle or forested environments
Summary
Yellow fever is an acute viral hemorrhagic disease transmitted by mosquitoes. Severity ranges from self-limited febrile illness to hemorrhagic syndrome with jaundice, multiple organ failure and death; severe cases are more likely to be detected and reported to passive surveillance systems [1,2]. The World Health Organization recommends vaccination of persons living in areas at-risk for yellow fever, as well as for epidemic control [3]. According to the 2010 revised yellow fever risk map, Brazil is one of 11 South American countries with endemic or transitional areas for yellow fever, and one of seven in which vaccine is recommended in only part of the territory [4]. In Brazil, yellow fever virus transmission is maintained in tropical forests in a sylvatic cycle first described in the 1930s [5], involving non-human primates and several species of tree-dwelling mosquitoes. Since several New World monkeys species develop fatal disease following yellow fever viral infection [2], sudden dieoffs of non-human primates may signal yellow fever virus circulation and a potential exposure risk to humans. In Brazil, sporadic human cases may occur as a result of recreational or occupational exposures to jungle areas [8,9]
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