Date Published: October 01, 2011
Publisher: The American Society of Tropical Medicine and Hygiene
Author(s): Andréa Barbosa de Melo, Maria da Paz C. da Silva, Maria Cecília F. Magalhães, Laura Helena Vega Gonzales Gil, Eduardo M. Freese de Carvalho, Ulisses M. Braga-Neto, Giovani Rota Bertani, Ernesto T. A. Marques, Marli Tenório Cordeiro.
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).
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
In the present study, we have established and analyzed the immunologic responses of a cohort of individuals living in Recife, Brazil, that had been vaccinated against YF with the 17DD vaccine. It is known that both the 17D and 17DD YFV vaccines induce long-lasting immunity in nearly 100% of individuals vaccinated with a single dose.2 The immunological profile of the 17DD vaccine has always been assumed to be identical to that of the 17D vaccine; however, a formal demonstration of the immunological profile of 17DD has been lacking in the scientific literature. In addition, it is not known if previous infection by dengue would interfere with the 17DD vaccine response. In our prospective study, all volunteers had neutralizing antibodies at 1 month after vaccination (GMT = 912); in the retrospective study, the same was true at 10 years post-vaccination (GMT = 113), although at much lower titers. These results are similar to those previously obtained with the 17D vaccine31 and suggest that a single dose of the YF-17DD vaccine may provide protection from wild-type YFV infection for at least 10 years, which is consistent with the World Health Organization (WHO) recommendation for international travel to YF-endemic areas. The minimum PRNT titer necessary guarantee protection is not clear, and because 35% of the individuals presented titers below 1:100 after 10 years post-vaccination, the WHO recommendation to repeat YFV immunization every 10 years is very reasonable.29,32