Evaluation of humoral immune response after yellow fever infection: an observational study on patients from the 2017-2018 sylvatic outbreak in Brazil.

Between 2016 and 2018, Brazil experienced major sylvatic yellow fever (YF) outbreaks that caused hundreds of casualties, with Minas Gerais (MG) being the most affected state. These outbreaks provided a unique opportunity to assess the immune response triggered by the wild-type (WT) yellow fever virus (YFV) in humans. The plaque reduction neutralization test (PRNT) is currently the standard method to assess the humoral immune response to YFV by measuring neutralizing antibodies (nAbs). The present study aimed to evaluate the humoral immune response of patients from the 2017-2018 sylvatic YF outbreak in MG with different disease outcomes by using PRNTs with a WT YFV strain, isolated from the 2017-2018 outbreak, and a vaccine YFV strain. Samples from naturally infected YF patients were tested, in comparison with healthy vaccinees. Results showed that both groups presented different levels of nAb against the WT and vaccine strains, and the levels of neutralization against the strains varied homotypically and heterotypically. Results based on the geometric mean titers (GMTs) suggest that the humoral immune response after a natural infection of YFV can reach higher levels than that induced by vaccination (GMT of patients against WT YFV compared to GMT of vaccinees, P < 0.0001). These findings suggest that the humoral immune responses triggered by the vaccine and WT strains of YFV are different, possibly due to genetic and antigenic differences between these viruses. Therefore, current means of assessing the immune response in naturally infected YF individuals and immunological surveillance methods in areas with intense viral circulation may need to be updated.IMPORTANCEYellow fever is a deadly febrile disease caused by the YFV. Despite the existence of effective vaccines, this disease still represents a public health concern worldwide. Much is known about the immune response against the vaccine strains of the YFV, but recent studies have shown that it differs from that induced by WT strains. The extent of this difference and the mechanisms behind it are still unclear. Thus, studies aimed to better understand the immune response against this virus are relevant and necessary. The present study evaluated levels of neutralizing antibodies of yellow fever patients from recent outbreaks in Brazil, in comparison with healthy vaccinees, using plaque reduction neutralization tests with WT and vaccine YFV strains. Results showed that the humoral immune response in naturally infected patients was higher than that induced by vaccination, thus providing new insights into the immune response triggered against these viruses.

Sofosbuvir Off-label Treatment of Yellow Fever Patients During an Outbreak in Brazil, 2018: A Cohort Study.

We enrolled 21 patients with laboratory-confirmed yellow fever (YF), hospitalized at Eduardo de Menezes Hospital, Brazil, to be treated with sofosbuvir, a drug approved for hepatitis C. Given the absence of specific YF antiviral treatments, the off-label nonrandomized sofosbuvir treatment aimed to address high disease severity and the risk of fatal outcomes. Patients received a daily dose of 400 mg sofosbuvir from 4 to 10 days post-symptom onset. YF viral load (VL) comparisons were made between treated and nontreated patients who either survived or died. The genomic VL for the treated group steadily decreased after day 7 post-symptom onset, suggesting that sofosbuvir might reduce YF VL. This study underscores the urgent need for YF antiviral therapies, advocating for randomized clinical trials to further explore sofosbuvir's role in YF treatment.

Yellow Fever Virus Genotyping Tool and Investigation of Suspected Adverse Events Following Yellow Fever Vaccination.

The yellow fever (YF) vaccine consists of an attenuated virus, and despite its relative safety, some adverse events following YF vaccination have been described. At the end of 2016, Brazil experienced the most massive sylvatic yellow fever outbreak over the last 70 years and an intense campaign of YF vaccination occurred in Minas Gerais state in Southeast Brazil from 2016 to 2018. The present study aimed to develop a genotyping tool and investigate 21 cases of suspected adverse events following YF vaccination. Initial in silico analyses were performed using partial NS5 nucleotide sequences to verify the discriminatory potential between wild-type and vaccine viruses. Samples from patients were screened for the presence of the YFV RNA, using 5'UTR as the target, and then used for amplification of partial NS5 gene amplification, sequencing, and phylogenetic analysis. Genotyping indicated that 17 suspected cases were infected by the wild-type yellow fever virus, but four cases remained inconclusive. The genotyping tool was efficient in distinguishing the vaccine from wild-type virus, and it has the potential to be used for the differentiation of all yellow fever virus genotypes.

Análise da reatividade contra as proteínas H1 e H3 dos vírus influenza América do Sul por ensaio imunoenzimático

A influenza é uma doença infecciosa respiratória aguda, causada pelos vírus influenza, que possui distribuição global e transmissibilidade elevada, sendo considerada a infecção viral de maior impacto no mundo. Entretanto, ainda é difícil quantificar a real incidência/prevalência dessa doença, uma vez que grande parte dos indivíduos infectados não procura atendimento médico, e, portanto, não é diagnosticada. Nesse contexto, a determinação direta da soroprevalência contra influenza pode gerar informações mais exatas sobre a doença. Os ensaios imunoenzimáticos permitem a detecção de anticorpos contra influenza e podem assim ser usados para estimar soroprevalência desses vírus em determinadas populações. Crianças e adolescentes representam importantes grupos de risco de infecção por influenza, por estarem mais expostos ao contato com esses vírus no ambiente escolar. Portanto, a avaliação de biomarcadores de infecções prévias por tais vírus nesses indivíduos configura uma boa oportunidade de se estimar o perfil de reatividade dessa população. Esse trabalho avaliou a reatividade do soro de adolescentes escolares residentes no Rio Grande do Sul, contra as proteínas H1 e H3 do influenza. Para isso, foi desenvolvido um ensaio imunoenzimático indireto, utilizando como antígenos as proteínas H1 e H3. As proteínas usadas foram produzidas por expressão em sistema E. coli, por meio do uso de vetores pET30a, nos quais foram subclonadas sequências gênicas de H1 e H3, geradas a partir de sequências consenso, montadas através do alinhamento de sequências de diferentes amostras virais de (H1N1)pdm e H3N2. A partir do ensaio imunoenzimático desenvolvido, 957 amostras de soro de adolescentes, entre 12 e 17 anos, que frequentavam escolas na cidade de Porto Alegre no Rio Grande do Sul foram testadas quanto à presença de anticorpos IgG contra as proteínas H1 e H3. Os resultados obtidos demonstraram que grande parte dessa população possui anticorpos contra os subtipos de influenza A, (H1N1)pdm09 e H3N2. Foi observada uma taxa de soropositividade geral entre os adolescentes de 78,47% para a proteína H1 e 80,67% para a proteína H3. As taxas elevadas de soropositividade observadas corroboram com dados publicados por outros países, nos quais também foram encontrados níveis de soropositividade para influenza entre 80 e 100% em populações jovens. A soropositividade elevada encontrada entre os escolares desse estudo sugere que essa população pode estar mais exposta às infecções por esses vírus e alerta sobre as consequências potenciais dessas infecções. Futuramente, as informações geradas por esse estudo poderão auxiliar na tomada de decisões de saúde pública para a implementação de estratégias de controle e prevenção da influenza na região sul do Brasil.