Abstract
From September 2005 to March 2007, 238 individuals being vaccinated for the first time with the yellow fever (YF) -17DD vaccine were enrolled in a cohort established in Recife, Brazil. A prospective study indicated that, after immunization, anti-YF immunoglobulin M (IgM) and anti-YF IgG were present in 70.6% (IgM) and 98.3% (IgG) of the vaccinated subjects. All vaccinees developed protective immunity, which was detected by the plaque reduction neutralization test (PRNT) with a geometric mean titer of 892. Of the 238 individuals, 86.6% had IgG antibodies to dengue virus; however, the presence of anti-dengue IgG did not interfere significantly with the development of anti-YF neutralizing antibodies. In a separate retrospective study of individuals immunized with the 17DD vaccine, the PRNT values at 5 and 10 years post-vaccination remained positive but showed a significant decrease in neutralization titer (25% with PRNT titers < 100 after 5 years and 35% after 10 years).
Highlights
Yellow fever (YF) is a viral illness transmitted by mosquitoes (Aedes and Haemagogus genera) infected with the YF virus (YFV), which belongs to the genus Flavivirus.The clinical manifestations of infection vary considerably, ranging from asymptomatic to classic forms of hemorrhagic fever, which are associated with high fatality rates.[1]
We have described the development of a YF cohort of vaccinated individuals living in Recife, the capital of the state of Pernambuco, Brazil, for use in studying the immune responses against the YF-17DD and evaluating possible effects of existing anti-dengue antibodies on the YF vaccine responses
To determine whether previous exposure to dengue had a significant effect on the YFV vaccination results, we investigated the presence of antidengue immunoglobulin G (IgG) in this cohort
Summary
Yellow fever (YF) is a viral illness transmitted by mosquitoes (Aedes and Haemagogus genera) infected with the YF virus (YFV), which belongs to the genus Flavivirus (family Flaviviridae).The clinical manifestations of infection vary considerably, ranging from asymptomatic to classic forms of hemorrhagic fever, which are associated with high fatality rates.[1]At present, the control of urban YFV transmission can be accomplished by vector control and vaccination. YF remains an endemic and epidemic problem affecting millions of people in tropical Africa and South America, especially those living at the fringe of urban and sylvatic environments. It is a continuing threat to people who travel to these regions without vaccination.[2] In Brazil, YF is endemic in extensive regions of the Amazon forest and the southwest of the country; YF vaccination is strongly recommended for travelers to these regions.[3] The boundary between these two zones is constantly affected by periodic expansions into areas of epizootic activity. YFV is transmitted in sparsely populated forested areas and affects mainly individuals engaged in clearing land for agriculture, ecological tourism, and other professional activities related to penetration of the jungle.[4] From 1980 to 2008, there were 723 confirmed YF cases of sylvatic origin, among which 389 deaths occurred, resulting in a 53.8% average lethality. Adult males were the most affected segment of the population.[3]
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