Single shot of 17D vaccine may not confer life-long protection against yellow fever

The yellow fever (YF) vaccine has been used since the 1930s to prevent YF, which is a severe infectious disease caused by the yellow fever virus (YFV), and mainly transmitted by Culicidae mosquitoes from the genera Aedes and Haemagogus . Until 2013, the World Health Organization (WHO) recommended the administration of a vaccine dose every ten years. A new recommendation of a single vaccine dose to confer life-long protection against YFV infection has since been established. Recent evidence published elsewhere suggests that at least a second dose is needed to fully protect against YF disease. Here, we discuss the feasibility of administering multiple doses, the necessity for a new and modern vaccine, and recommend that the WHO conveys a meeting to discuss YFV vaccination strategies for people living in or travelling to endemic areas.

Prevalence and titers of yellow fever virus neutralizing antibodies in previously vaccinated adults

ABSTRACT Introduction: The World Health Organization (WHO) recommends one single dose of the Yellow Fever (YF) vaccine based on studies of antibody persistency in healthy adults. We assessed the prevalence and titers of YF virus neutralizing antibodies in previously vaccinated persons aged ≥ 60 years, in comparison to younger adults. We also evaluated the correlation between antibody titers and the time since vaccination among participants who received one vaccine dose, and the seropositivity among participants vaccinated prior to or within the past 10 years. Methods: previously vaccinated healthy persons aged ≥ 18 years were included. YF virus neutralizing antibody titers were determined by means of the 50% Plaque Reduction Neutralization Test. Results: 46 persons aged ≥ 60 years and 48 persons aged 18 to 59 years were enrolled. There was no significant difference in the prevalence of YF virus neutralizing antibodies between the two groups (p = 0.263). However, titers were significantly lower in the elderly (p = 0.022). There was no correlation between YF virus neutralizing antibody titers and the time since vaccination. There was no significant difference in seropositivity among participants vaccinated prior to or within the past 10 years. Conclusions: the clinical relevance of the observed difference in YF virus neutralizing antibody titers between the two groups is not clear.

A randomised double-blind clinical trial of two yellow fever vaccines prepared with substrains 17DD and 17D-213/77 in children nine-23 months old

This randomised, double-blind, multicentre study with children nine-23 months old evaluated the immunogenicity of yellow fever (YF) vaccines prepared with substrains 17DD and 17D-213/77. YF antibodies were tittered before and 30 or more days after vaccination. Seropositivity and seroconversion were analysed according to the maternal serological status and the collaborating centre. A total of 1,966 children were randomised in the municipalities of the states of Mato Grosso do Sul, Minas Gerais and São Paulo and blood samples were collected from 1,714 mothers. Seropositivity was observed in 78.6% of mothers and 8.9% of children before vaccination. After vaccination, seropositivity rates of 81.9% and 83.2%, seroconversion rates of 84.8% and 85.8% and rates of a four-fold increase over the pre-vaccination titre of 77.6% and 81.8% were observed in the 17D-213/77 and 17DD subgroups, respectively. There was no association with maternal immunity. Among children aged 12 months or older, the seroconversion rates of 69% were associated with concomitant vaccination against measles, mumps and rubella. The data were not conclusive regarding the interference of maternal immunity in the immune response to the YF vaccine, but they suggest interference from other vaccines. The failures in seroconversion after vaccination support the recommendation of a booster dose in children within 10 years of the first dose.

Serologic assessment of yellow fever immunity in the rural population of a yellow fever-endemic area in Central Brazil

Introduction The yellow fever epidemic that occurred in 1972/73 in Central Brazil surprised the majority of the population unprotected. A clinical-epidemiological survey conducted at that time in the rural area of 19 municipalities found that the highest (13.8%) number of disease cases were present in the municipality of Luziânia, State of Goiás. Methods Thirty-eight years later, a new seroepidemiological survey was conducted with the aim of assessing the degree of immune protection of the rural population of Luziânia, following the continuous attempts of public health services to obtain vaccination coverage in the region. A total of 383 volunteers, aged between 5 and 89 years and with predominant rural labor activities (75.5%), were interviewed. The presence of antibodies against the yellow fever was also investigated in these individuals, by using plaque reduction neutralization test, and correlated to information regarding residency, occupation, epidemiological data and immunity against the yellow fever virus. Results We found a high (97.6%) frequency of protective titers (>1:10) of neutralizing antibodies against the yellow fever virus; the frequency of titers of 1:640 or higher was 23.2%, indicating wide immune protection against the disease in the study population. The presence of protective immunity was correlated to increasing age. Conclusions This study reinforces the importance of surveys to address the immune state of a population at risk for yellow fever infection and to the surveillance of actions to control the disease in endemic areas. .

Dengue-2 and yellow fever 17DD viruses infect human dendritic cells, resulting in an induction of activation markers, cytokines and chemokines and secretion of different TNF-α and IFN-α profiles

Flaviviruses cause severe acute febrile and haemorrhagic infections, including dengue and yellow fever and the pathogenesis of these infections is caused by an exacerbated immune response. Dendritic cells (DCs) are targets for dengue virus (DENV) and yellow fever virus (YF) replication and are the first cell population to interact with these viruses during a natural infection, which leads to an induction of protective immunity in humans. We studied the infectivity of DENV2 (strain 16681), a YF vaccine (YF17DD) and a chimeric YF17D/DENV2 vaccine in monocyte-derived DCs in vitro with regard to cell maturation, activation and cytokine production. Higher viral antigen positive cell frequencies were observed for DENV2 when compared with both vaccine viruses. Flavivirus-infected cultures exhibited dendritic cell activation and maturation molecules. CD38 expression on DCs was enhanced for both DENV2 and YF17DD, whereas OX40L expression was decreased as compared to mock-stimulated cells, suggesting that a T helper 1 profile is favoured. Tumor necrosis factor (TNF)-α production in cell cultures was significantly higher in DENV2-infected cultures than in cultures infected with YF17DD or YF17D/DENV. In contrast, the vaccines induced higher IFN-α levels than DENV2. The differential cytokine production indicates that DENV2 results in TNF induction, which discriminates it from vaccine viruses that preferentially stimulate interferon expression. These differential response profiles may influence the pathogenic infection outcome.

Anticuerpos neutralizantes contra el virus de la fiebre amarilla 17 D en colombianos vacunados y no vacunados con inmunidad a dengue / Yellow fever virus 17D neutralising antibodies in vaccinated Colombian people and unvaccinated ones having immunity against dengue

Objetivo Determinar la frecuencia de título protector de anticuerpos neutralizantes contra el virus de la fiebre amarilla (AN-VFA a título >1:10) en colombianos vacunados con la cepa 17 D y conocer la magnitud de neutralización del VFA por anticuerpos contra dengue. Metodología Se colectó suero de 100 individuos con vacuna documentada por carné y de 116 residentes en municipios de Norte de Santander afectados por el brote en 2002-2003, quienes informaron haber sido vacunados. Se incluyeron sueros de individuos no vacunados con (n=61) y sin (n=16) anticuerpos contra dengue. Todos los sueros se analizaron por la prueba de neutralización para VFA por 75 por ciento de reducción de placa. Resultados AN-VFA a título >1:10 se encontraron en 90 por ciento de vacunados con carné y sin variación aparente en relación con edad. Al contrario, hubo correlación entre disminución de la frecuencia de título protector de anticuerpos e incremento del tiempo de inmunización (r=0,95; p=0,04). En residentes de Norte de Santander, AN-VFA a título >1:10 se encontraron en 92,6 por ciento adultos y 69 por ciento niños. El VFA fue neutralizado (52 -100 por ciento) por sueros de inmunes a dengue más eficientemente que por sueros de no inmunes (p<0.001). Conclusiones Vacunados con el virus 17 D podrían no estar protegidos contra fiebre amarilla: hasta 31 por ciento niños y 10 por ciento adultos. Anticuerpos contra dengue inhibieron el VFA y su significancia en términos de protección contra fiebre amarilla deberá ser investigada.

Objective Determining the frequency of yellow fever seroprotective antibody neutralising titres (YF-NT >1:10) in Colombians vaccinated with the 17 D virus and ascertaining the extent to which YF virus can be neutralised by dengue antibodies. Materials and Methods Serum samples were taken from 100 subjects who showed their vaccination record and from 116 residents in municipalities (Norte de Santander) affected by a wild YF outbreak in 2002-2003 who were reported to have been YF vaccinated. Sera from individuals with (n=61) and without (n=16) dengue antibodies who had never been YF vaccinated were included. All the sera were tested by 75 percent YF plaque-reduction neutralization test. Results YF-NT titres >1:10 were founded in 90 percent of subjects with vaccination recorded with minors variations in relation to age. In contrast, there was correlation between decrease of seroprotective YF-NT titres frequency and increase of immunization time (r=0.95; p=0.04). In residents in YF endemic area, YF-NT titres > 1.10 were founded in 92,6 percent adults and 69 percent children. YF 17 D virus was neutralized (52-100 percent) by dengue sera more efficiently than non-dengue immune sera (p<0.001). Conclusions Individuals immunised with YF vaccine 17 D could not be protected against YF: up to 31 percent children and 10 percent adults. Dengue antibodies inhibited YF virus and its significance in terms of YF protection must be investigated.

Limited replication of yellow fever 17DD and 17D-Dengue recombinant viruses in rhesus monkeys

For the development of safe live attenuated flavivirus vaccines one of the main properties to be established is viral replication. We have used real-time reverse transcriptase-polymerase chain reaction and virus titration by plaque assay to determine the replication of yellow fever 17DD virus (YFV 17DD) and recombinant yellow fever 17D viruses expressing envelope proteins of dengue virus serotypes 2 and 4 (17D-DENV-2 and 17D-DENV-4). Serum samples from rhesus monkeys inoculated with YFV 17DD and 17D-DENV chimeras by intracerebral or subcutaneous route were used to determine and compare the viremia induced by these viruses. Viral load quantification in samples from monkeys inoculated by either route with YFV 17DD virus suggested a restricted capability of the virus to replicate reaching not more than 2.0 log10 PFU mL-1 or 3.29 log10 copies mL-1. Recombinant 17D-dengue viruses were shown by plaquing and real-time PCR to be as attenuated as YF 17DD virus with the highest mean peak titer of 1.97 log10 PFU mL-1 or 3.53 log10 copies mL-1. These data serve as a comparative basis for the characterization of other 17D-based live attenuated candidate vaccines against other diseases.

Uma das principais propriedades a serem estabelecidas para o desenvolvimento de vacinas seguras e atenuadas de flavivirus,é a taxa de replicação viral. Neste trabalho, aplicamos a metodologia de amplificação pela reação em cadeia da polimerase em tempo real e titulação viral por plaqueamento para determinação da replicação do vírus 17DD (FA 17DD) e recombinantes, expressando proteínas do envelope de dengue sorotipos 2 e 4 (17D-DENV-2 e 17D-DENV-4). As amostras de soros de macacos inoculados por via intracerebral ou subcutânea com FA 17DD ou 17D-DENV foram usadas para determinar e comparar a viremia induzida por estes vírus. A quantificação da carga viral em amostras de macacos inoculados por ambas as vias com FA 17DD sugere restrita capacidade de replicação com taxa não superior a 2,0 log10 PFU mL-1 ou 3,29 log10 cópias/mL-1. Os vírus recombinantes 17D-DENV mostraram-se tão atenuados quanto o vírus 17DD, tanto porRT-PCR em tempo real quanto por plaqueamento, com título médio máximo de 1,97 log10 PFU mL-1 ou 3,53 log10 cópias/mL-1. Estes dados servem como base comparativapara caracterização de outros vírus vivos atenuados, derivados do vírus 17D, candidatos a vacinas contra outras doenças.

The sample processing time interval as an influential factor in flow cytometry analysis of lymphocyte subsets

The objective of this paper is to propose a protocol to analyze blood samples in yellow fever 17DD vaccinated which developed serious adverse events. We investigated whether or not the time between sample collection and sample processing could interfere in lymphocyte subset percentage, for it is often impossible to analyze blood samples immediately after collection due to transport delay from collection places to the flow cytometry facility. CD4+CD38+ T, CD8+CD38+ T, CD3+ T, CD19+ B lymphocyte subsets were analyzed by flow cytometry in nine healthy volunteers immediately after blood collection and after intervals of 24 and 48 h. The whole blood lysis method and gradient sedimentation by Histopaque were applied to isolate peripheral blood mononuclear cells for flow cytometry analyses. With the lysis method, there was no significant change in lymphocyte subset percentage between the two time intervals (24 and 48 h). In contrast, when blood samples were processed by Histopaque gradient sedimentation, time intervals for sample processing influenced the percentage in T lymphocyte subsets but not in B cells. From the results obtained, we could conclude that the whole blood lysis method is more appropriate than gradient sedimentation by Histopaque for immunophenotyping of blood samples collected after serious adverse events, due to less variation in the lymphocyte subset levels with respect to the time factor.

Aplicação de PCR em tempo real para avaliar viremia em humanos e primatas não humanos, imunizados com a vacina de febre amarela cepa 17DD e o vírus recombinante 17D-DENV / Application of PCR in real time to evaluate viremia in human beings and not human primates, immunized with the vaccine of yellow fever cepa 17DD and recombinant virus 17D-DENV

Um dos parâmetros principais para o estudo de atenuação de flavivírus é a determinação de sua capacidade de replicação. Neste contexto, empregamos o método de RT-PCR em tempo real que permite a detecção de ácidos nucléicos diretamente de amostras biológicas. Neste trabalho, utilizamos, então, esta tecnologia, para determinar a replicação de vírus de febre amarela 17DD e 17D-recombinantes, que expressam a proteína do envelope dos vírus dengue para validação destes como candidatos a vacinas. Esta metodologia foi empregada de forma complementar ao teste clássico de titulação viral por plaqueamento em culturas de células de vertebrados. Os materiais clínicos incluem soros de macacos rhesus previamente inoculados com estes vírus por via intracerebral ou subcutânea e soros de 32 indivíduos vacinados com vírus 17DD. O método demonstrou boa reprodutibilidade para amostras com título viral de até 2 Log10 PFU/mL com limite de detecção de até 10 PFU/mL ou 143 cópias /mL, sendo esta sensibilidade comparável ao que foi descrito para outros vírus analisados pela mesma tecnologia. Nesta faixa de concentração, os resultados obtidos pela metodologia de RT-PCR em tempo real mostraram-se compatíveis com os obtidos pelas técnicas de RT-PCR “semi nested” e pelo plaqueamento em soros de macacos inoculados com vírus 17DD. A análise comparativa da quantificação viral em espécimes clínicos de macacos sugere a limitada capacidade de replicação do vírus 17DD independente da via de inoculação. Os vírus 17D-recombinantes, avaliados neste estudo, demonstraram sua atenuação em relação ao vírus 17DD, tanto pela metodologia de RT-PCR em tempo real como por plaqueamento. Assim sendo, consideramos que a tecnologia empregada para o estudo da capacidade replicativa dos vírus 17DD e 17D-recombinantes em diferentes hospedeiros, demonstrou o perfil de atenuação dos vírus testados. Com relação aos vírus recombinantes 17D-dengue, estes resultados embasam a continuação do seu desenvolvimento como cand...

Lymphocyte subset analyses in healthy adults vaccinated with yellow fever 17DD virus

In this study the kinetics of humoral and cellular immune responses in first-time vaccinees and re-vaccinees with the yellow fever 17DD vaccine virus was analyzed. Flow cytometric analyses were used to determine percentual values of T and B cells in parallel to the yellow fever neutralizing antibody production. All lymphocyte subsets analyzed were augmented around the 30th post vaccination day, both for first-time vaccinees and re-vaccinees. CD3+ T cells increased from 30.8 percent (SE ± 4 percent) to 61.15 percent (SE ± 4.2 percent), CD4+ T cells from 22.4 percent (SE ± 3.6 percent) to 39.17 percent (SE ± 2 percent) with 43 percent of these cells corresponding to CD4+CD45RO+ T cells, CD8+ T cells from 15.2 percent (SE ± 2.9 percent) to 27 percent (SE ± 3 percent) with 70 percent corresponding to CD8+CD45RO+ T cells in first-time vaccinees. In re-vaccinees, the CD3+ T cells increased from 50.7 percent (SE ± 3 percent) to 80 percent (SE ± 2.3 percent), CD4+ T cells from 24.9 percent (SE ± 1.4 percent) to 40 percent (SE ± 3 percent) presenting a percentage of 95 percent CD4+CD45RO+ T cells, CD8+ T cells from 19.7 percent (SE ± 1.8 percent) to 25 percent (SE ± 2 percent). Among CD8+CD38+ T cells there could be observed an increase from 15 to 41.6 percent in first-time vaccinees and 20.7 to 62.6 percent in re-vaccinees. Regarding neutralizing antibodies, the re-vaccinees presented high titers even before re-vaccination. The levels of neutralizing antibodies of first-time vaccinees were similar to those presented by re-vaccinees at day 30 after vaccination, indicating the success of primary vaccination. Our data provide a basis for further studies on immunological behavior of the YF 17DD vaccine.