Akira Homma, Christiane de Roode Torres, Cyomara de Jesus Bianchini, Armando Pires, Aline de Alcântara Vinhast, Jandira Aparecida Campos Lemos, José Ailton de Souza Martins, João Silveira Cruz, Cristina Toscano Fonseca, Maria Rios, Rita Maria Ribeiro Nogueira, Robson de Souza Leite Cruz, Harold Richard Persi, Valéria Lúcia de Sousa Gil, Andréa Teixeira Carvalho, Tatiane Rocha Alves, Maria de Lourdes de Sousa Maia, Shirley da Silva de Moraes, Reinaldo de Menezes Martins, Luanda Machado, Elizabeth Maciel de Albuquerque, Eliane Santos Matos, Vanessa dos Reis von Doellinger, Jociara Silva Santos, Tatiana Nogueira Noronha, Maria Camello de Paiva, Pedro Fernando da Costa Vasconcelos, Dayana Cristina Vieira de Souza, Minas Gerais. Secretaria Estadual de Saude. Belo Horizonte, Mg, Brasil, Anna Maya Yoshida, Luiz Cosme Cotta Malaquias, Marcos Dornelas Ribeiro, Ana Maria Bispo de Filippis, Roberto Henrique Guedes Farias, Pedro Luiz Tauil, Ana Carolina Campi Azevedo, Lis Ribeiro do Valle Antonelli, Olindo Assis Martins Filho, Mirian Mariano de Souza, Luiz Antonio Bastos Camacho, Adelayde S. Bastos, Cynthia Esteves, Azola Costa Ribeiro e Ribeiro, Ana Maria Basílio da Silva, Jorge Marcelo Rodrigues Pereira, Mauricio Ferreira Pimenta, Iramaya Rodrigues Caldas, Claudemir Francisco da Cunha Junior, Raiany Araujo Santos, Luiza Pacheco Porto, Marisol Simões, Thiago Campos Cabral, Carolina S. Carvalho, Eliane Araújo, Elena Cristina Caride Siqueira Campos, and Marcos da Silva Freire
INTRODUCTION: Available scientific evidence to recommend or to advise against booster doses of yellow fever vaccine (YFV) is inconclusive. A study to estimate the seropositivity rate and geometric mean titres (GMT) of adults with varied times of vaccination was aimed to provide elements to revise the need and the timing of revaccination. METHODS: Adults from the cities of Rio de Janeiro and Alfenas located in non-endemic areas in the Southeast of Brazil, who had one dose of YFV, were tested for YF neutralising antibodies and dengue IgG. Time (in years) since vaccination was based on immunisation cards and other reliable records. RESULTS: From 2011 to 2012 we recruited 691 subjects (73% males), aged 18-83 years. Time since vaccination ranged from 30 days to 18 years. Seropositivity rates (95%C.I.) and GMT (International Units/mL; 95%C.I.) decreased with time since vaccination: 93% (88-96%), 8.8 (7.0-10.9) IU/mL for newly vaccinated; 94% (88-97), 3.0 (2.5-3.6) IU/mL after 1-4 years; 83% (74-90), 2.2 (1.7-2.8) IU/mL after 5-9 years; 76% (68-83), 1.7 (1.4-2.0) IU/mL after 10-11 years; and 85% (80-90), 2.1 (1.7-2.5) IU/mL after 12 years or more. YF seropositivity rates were not affected by previous dengue infection. CONCLUSIONS:Eventhough serological correlates of protection for yellow fever are unknown, seronegativity in vaccinated subjects may indicate primary immunisation failure, or waning of immunity to levels below the protection threshold. Immunogenicity of YFV under routine conditions of immunisation services is likely to be lower than in controlled studies. Moreover, infants and toddlers, who comprise the main target group in YF endemic regions, and populations with high HIV infection rates, respond to YFV with lower antibody levels. In those settings one booster dose, preferably sooner than currently recommended, seems to be necessary to ensure longer protection for all vaccinees