FluoRNT: A robust, efficient assay for the detection of neutralising antibodies against yellow fever virus 17D.

There is an urgent need for better diagnostic and analytical methods for vaccine research and infection control in virology. This has been highlighted by recently emerging viral epidemics and pandemics (Zika, SARS-CoV-2), and recurring viral outbreaks like the yellow fever outbreaks in Angola and the Democratic Republic of Congo (2016) and in Brazil (2016-2018). Current assays to determine neutralising activity against viral infections in sera are costly in time and equipment and suffer from high variability. Therefore, both basic infection research and diagnostic population screenings would benefit from improved methods to determine virus-neutralising activity in patient samples. Here we describe a robust, objective, and scalable Fluorescence Reduction Neutralisation Test (FluoRNT) for yellow fever virus, relying on flow cytometric detection of cells infected with a fluorescent Venus reporter containing variant of the yellow fever vaccine strain 17D (YF-17D-Venus). It accurately measures neutralising antibody titres in human serum samples within as little as 24 h. Samples from 32 vaccinees immunised with YF-17D were tested for neutralising activity by both a conventional focus reduction neutralisation test (FRNT) and FluoRNT. Both types of tests proved to be equally reliable for the detection of neutralising activity, however, FluoRNT is significantly more precise and reproducible with a greater dynamic range than conventional FRNT. The FluoRNT assay protocol is substantially faster, easier to control, and cheaper in per-assay costs. FluoRNT additionally reduces handling time minimising exposure of personnel to patient samples. FluoRNT thus brings a range of desirable features that can accelerate and standardise the measurement of neutralising anti-yellow fever virus antibodies. It could be used in applications ranging from vaccine testing to large cohort studies in systems virology and vaccinology. We also anticipate the potential to translate the methodology and analysis of FluoRNT to other flaviviruses such as West Nile, Dengue and Zika or to RNA viruses more generally.

High-Throughput Platform for Detection of Neutralizing Antibodies Using Flavivirus Reporter Replicon Particles.

Flavivirus outbreaks require fast and reliable diagnostics that can be easily adapted to newly emerging and re-emerging flaviviruses. Due to the serological cross-reactivity among flavivirus antibodies, neutralization tests (NT) are considered the gold standard for sero-diagnostics. Here, we first established wild-type single-round infectious virus replicon particles (VRPs) by packaging a yellow fever virus (YFV) replicon expressing Gaussia luciferase (Gluc) with YFV structural proteins in trans using a double subgenomic Sindbis virus (SINV) replicon. The latter expressed the YFV envelope proteins prME via the first SINV subgenomic promoter and the capsid protein via a second subgenomic SINV promoter. VRPs were produced upon co-electroporation of replicon and packaging RNA. Introduction of single restriction enzyme sites in the packaging construct flanking the prME sequence easily allowed to exchange the prME moiety resulting in chimeric VRPs that have the surface proteins of other flaviviruses including dengue virus 1--4, Zika virus, West Nile virus, and tick-borne encephalitis virus. Besides comparing the YF-VRP based NT assay to a YF reporter virus NT assay, we analyzed the neutralization efficiencies of different human anti-flavivirus sera or a monoclonal antibody against all established VRPs. The assays were performed in a 96-well high-throughput format setting with Gluc as readout in comparison to classical plaque reduction NTs indicating that the VRP-based NT assays are suitable for high-throughput analyses of neutralizing flavivirus antibodies.

Even old foes can learn sweet new tricks.

In this issue of Cell Host and Microbe, Haslwanter et al. (2022) present a comprehensive investigation into the molecular and functional basis of 17D vaccine responses and into differences between antibody neutralization of the 17D and related African lineage strains to contemporary Central/South American strains, including the emergent YFV ES-504 strain.

An evaluation of the diagnostic performance characteristics of the Yellow Fever IgM immunochromatographic rapid diagnostic test kit from SD Biosensor in Ghana.

Yellow fever is endemic in Ghana and outbreaks occur periodically. The prodromal signs due to Yellow Fever Virus (YFV) infection are non-specific, making clinical signs unreliable as the sole criteria for diagnosis. Accurate laboratory confirmation of suspected yellow fever cases is therefore vital in surveillance programs. Reporting of ELISA IgM testing results by laboratories can delay due to late arrival of samples from the collection sites as well as limited availability of ELISA kits. In this study, the diagnostic performance characteristics of a rapid immunochromatographic Standard Q Yellow Fever IgM test kit (SD Biosensor) was evaluated for the rapid diagnosis of Yellow Fever infection in Ghana. A panel of 275 sera, comprising 81 confirmed YFV positives and 194 negatives were re-tested in this study using the Standard Q Yellow Fever IgM test kit. Using the CDC/WHO Yellow Fever IgM capture ELISA as a benchmark, the sensitivity, specificity and accuracy of the Standard Q Yellow Fever test kit were 96.3%, 97.9% and 97.5%, respectively. The false positivity rate was 5.1% and there was no cross-reactivity when the Standard Q Yellow Fever test kit was tested against dengue, malaria and hepatitis B and C positive samples. In addition, inter-reader variability and invalid rate were both zero. The results indicate that the diagnostic performance of the Standard Q Yellow Fever IgM test kit on serum or plasma is comparable to the serum IgM detection by ELISA and can be used as a point of care rapid diagnostic test kit for YFV infection in endemic areas.

A yellow fever virus NS4B inhibitor not only suppresses viral replication, but also enhances the virus activation of RIG-I-like receptor-mediated innate immune response.

Flavivirus infection of cells induces massive rearrangements of the endoplasmic reticulum (ER) membrane to form viral replication organelles (ROs) which segregates viral RNA replication intermediates from the cytoplasmic RNA sensors. Among other viral nonstructural (NS) proteins, available evidence suggests for a prominent role of NS4B, an ER membrane protein with multiple transmembrane domains, in the formation of ROs and the evasion of the innate immune response. We previously reported a benzodiazepine compound, BDAA, which specifically inhibited yellow fever virus (YFV) replication in cultured cells and in vivo in hamsters, with resistant mutation mapped to P219 of NS4B protein. In the following mechanistic studies, we found that BDAA specifically enhances YFV induced inflammatory cytokine response in association with the induction of dramatic structural alteration of ROs and exposure of double-stranded RNA (dsRNA) in virus-infected cells. Interestingly, the BDAA-enhanced cytokine response in YFV-infected cells is attenuated in RIG-I or MAD5 knockout cells and completely abolished in MAVS knockout cells. However, BDAA inhibited YFV replication at a similar extent in the parent cells and cells deficient of RIG-I, MDA5 or MAVS. These results thus provided multiple lines of biological evidence to support a model that BDAA interaction with NS4B may impair the integrity of YFV ROs, which not only inhibits viral RNA replication, but also promotes the release of viral RNA from ROs, which consequentially activates RIG-I and MDA5. Although the innate immune enhancement activity of BDAA is not required for its antiviral activity in cultured cells, its dual antiviral mechanism is unique among all the reported antiviral agents thus far and warrants further investigation in animal models in future.

Comparing immunogenicity and protective efficacy of the yellow fever 17D vaccine in mice.

The live-attenuated yellow fever 17D (YF17D) vaccine is one of the most efficacious human vaccines and also employed as a vector for novel vaccines. However, in the lack of appropriate immunocompetent small animal models, mechanistic insight in YF17D-induced protective immunity remains limited. To better understand YF17D vaccination and to identify a suitable mouse model, we evaluated the immunogenicity and protective efficacy of YF17D in five complementary mouse models, i.e. wild-type (WT) BALB/c, C57BL/6, IFN-α/ß receptor (IFNAR-/-) deficient mice, and in WT mice in which type I IFN signalling was temporally ablated by an IFNAR blocking (MAR-1) antibody. Alike in IFNAR-/- mice, YF17D induced in either WT mice strong humoral immune responses dominated by IgG2a/c isotype (Th1 type) antibodies, yet only when IFNAR was blocked. Vigorous cellular immunity characterized by CD4+ T-cells producing IFN-γ and TNF-α were mounted in MAR-1 treated C57BL/6 and in IFNAR-/- mice. Surprisingly, vaccine-induced protection was largely mouse model dependent. Full protection against lethal intracranial challenge and a massive reduction of virus loads was conferred already by a minimal dose of 2 PFU YF17D in BALB/c and IFNAR-/- mice, but not in C57BL/6 mice. Correlation analysis of infection outcome with pre-challenge immunological markers indicates that YFV-specific IgG might suffice for protection, even in the absence of detectable levels of neutralizing antibodies. Finally, we propose that, in addition to IFNAR-/- mice, C57BL/6 mice with temporally blocked IFN-α/ß receptors represent a promising immunocompetent mouse model for the study of YF17D-induced immunity and evaluation of YF17D-derived vaccines.

Yellow fever vaccine protects mice against Zika virus infection.

Zika virus (ZIKV) emerged as an important infectious disease agent in Brazil in 2016. Infection usually leads to mild symptoms, but severe congenital neurological disorders and Guillain-Barré syndrome have been reported following ZIKV exposure. Creating an effective vaccine against ZIKV is a public health priority. We describe the protective effect of an already licensed attenuated yellow fever vaccine (YFV, 17DD) in type-I interferon receptor knockout mice (A129) and immunocompetent BALB/c and SV-129 (A129 background) mice infected with ZIKV. YFV vaccination provided protection against ZIKV, with decreased mortality in A129 mice, a reduction in the cerebral viral load in all mice, and weight loss prevention in BALB/c mice. The A129 mice that were challenged two and three weeks after the first dose of the vaccine were fully protected, whereas partial protection was observed five weeks after vaccination. In all cases, the YFV vaccine provoked a substantial decrease in the cerebral viral load. YFV immunization also prevented hippocampal synapse loss and microgliosis in ZIKV-infected mice. Our vaccine model is T cell-dependent, with AG129 mice being unable to tolerate immunization (vaccination is lethal in this mouse model), indicating the importance of IFN-γ in immunogenicity. To confirm the role of T cells, we immunized nude mice that we demonstrated to be very susceptible to infection. Immunization with YFV and challenge 7 days after booster did not protect nude mice in terms of weight loss and showed partial protection in the survival curve. When we evaluated the humoral response, the vaccine elicited significant antibody titers against ZIKV; however, it showed no neutralizing activity in vitro and in vivo. The data indicate that a cell-mediated response promotes protection against cerebral infection, which is crucial to vaccine protection, and it appears to not necessarily require a humoral response. This protective effect can also be attributed to innate factors, but more studies are needed to strengthen this hypothesis. Our findings open the way to using an available and inexpensive vaccine for large-scale immunization in the event of a ZIKV outbreak.

Dynamics and turnover of memory CD8 T cell responses following yellow fever vaccination.

Understanding how immunological memory lasts a lifetime requires quantifying changes in the number of memory cells as well as how their division and death rates change over time. We address these questions by using a statistically powerful mixed-effects differential equations framework to analyze data from two human studies that follow CD8 T cell responses to the yellow fever vaccine (YFV-17D). Models were first fit to the frequency of YFV-specific memory CD8 T cells and deuterium enrichment in those cells 42 days to 1 year post-vaccination. A different dataset, on the loss of YFV-specific CD8 T cells over three decades, was used to assess out of sample predictions of our models. The commonly used exponential and bi-exponential decline models performed relatively poorly. Models with the cell loss following a power law (exactly or approximately) were most predictive. Notably, using only the first year of data, these models accurately predicted T cell frequencies up to 30 years post-vaccination. Our analyses suggest that division rates of these cells drop and plateau at a low level (0.1% per day, ∼ double the estimated values for naive T cells) within one year following vaccination, whereas death rates continue to decline for much longer. Our results show that power laws can be predictive for T cell memory, a finding that may be useful for vaccine evaluation and epidemiological modeling. Moreover, since power laws asymptotically decline more slowly than any exponential decline, our results help explain the longevity of immune memory phenomenologically.

Zika Virus Non-Structural Protein 1 Antigen-Capture Immunoassay.

Infection with Zika virus (ZIKV), a member of the Flavivirus genus of the Flaviviridae family, typically results in mild self-limited illness, but severe neurological disease occurs in a limited subset of patients. In contrast, serious outcomes commonly occur in pregnancy that affect the developing fetus, including microcephaly and other major birth defects. The genetic similarity of ZIKV to other widespread flaviviruses, such as dengue virus (DENV), presents a challenge to the development of specific ZIKV diagnostic assays. Nonstructural protein 1 (NS1) is established for use in immunodiagnostic assays for flaviviruses. To address the cross-reactivity of ZIKV NS1 with proteins from other flaviviruses we used site-directed mutagenesis to modify putative epitopes. Goat polyclonal antibodies to variant ZIKV NS1 were affinity-purified to remove antibodies binding to the closely related NS1 protein of DENV. An antigen-capture ELISA configured with the affinity-purified polyclonal antibody showed a linear dynamic range between approximately 500 and 30 ng/mL, with a limit of detection of between 1.95 and 7.8 ng/mL. NS1 proteins from DENV, yellow fever virus, St. Louis encephalitis virus and West Nile virus showed significantly reduced reactivity in the ZIKV antigen-capture ELISA. Refinement of approaches similar to those employed here could lead to development of ZIKV-specific immunoassays suitable for use in areas where infections with related flaviviruses are common.

Genome Characterization of Yellow Fever Virus Wild-Type Strain Asibi, Parent to Live-Attenuated 17D Vaccine, from Three Different Sources.

The yellow fever virus vaccine, 17D, was derived through the serial passage of the wild-type (WT) strain Asibi virus in mouse and chicken tissue. Since its derivation, the mechanism of attenuation of 17D virus has been investigated using three 17D substrains and WT Asibi virus. Although all three substrains of 17D have been sequenced, only one isolate of Asibi has been examined genetically and all interpretation of attenuation is based on this one isolate. Here, we sequenced the genome of Asibi virus from three different laboratories and show that the WT strain is genetically homogenous at the amino acids that distinguish Asibi from 17D vaccine virus.

Diffusion of sylvatic yellow fever in the state of São Paulo, Brazil.

We investigated the sylvatic yellow fever (SYF) diffusion process in São Paulo (SP) between 2016 and 2019. We developed an ecological study of SYF through autochthonous human cases and epizootics of non-human primates (NHPs) that were spatiotemporally evaluated. We used kriging to obtain maps with isochrones representative of the evolution of the outbreak and characterized its diffusion pattern. We confirmed 648 human cases of SYF in SP, with 230 deaths and 843 NHP epizootics. Two outbreak waves were identified: one from West to East (2016 and 2017), and another from the Campinas region to the municipalities bordering Rio de Janeiro, Minas Gerais, and Paraná and those of the SP coast (2017-2019). The SYF outbreak diffusion process was by contagion. The disease did not exhibit jumps between municipalities, indicating that the mosquitoes and NHPs were responsible for transmitting the virus. There were not enough vaccines to meet the population at risk; hence, health authorities used information about the epizootic occurrence in NHPs in forest fragments to identify priority populations for vaccination.

Activation and Kinetics of Circulating T Follicular Helper Cells, Specific Plasmablast Response, and Development of Neutralizing Antibodies following Yellow Fever Virus Vaccination.

A single dose of the replication-competent, live-attenuated yellow fever virus (YFV) 17D vaccine provides lifelong immunity against human YFV infection. The magnitude, kinetics, and specificity of B cell responses to YFV 17D are relatively less understood than T cell responses. In this clinical study, we focused on early immune events critical for the development of humoral immunity to YFV 17D vaccination in 24 study subjects. More specifically, we studied the dynamics of several immune cell populations over time and the development of neutralizing Abs. At 7 d following vaccination, YFV RNA in serum as well as several antiviral proteins were detected as a sign of YFV 17D replication. Activation of Th1-polarized circulating T follicular helper cells followed germinal center activity, the latter assessed by the surrogate marker CXCL13 in serum. This coincided with a plasmablast expansion peaking at day 14 before returning to baseline levels at day 28. FluoroSpot-based analysis confirmed that plasmablasts were specific to the YFV-E protein. The frequencies of plasmablasts correlated with the magnitude of neutralizing Ab titers measured at day 90, suggesting that this transient B cell subset could be used as an early marker of induction of protective immunity. Additionally, YFV-specific memory B cells were readily detectable at 28 and 90 d following vaccination, and all study subjects tested developed protective neutralizing Ab titers. Taken together, these studies provide insights into key immune events leading to human B cell immunity following vaccination with the YFV 17D vaccine.

Prior Heterologous Flavivirus Exposure Results in Reduced Pathogenesis in a Mouse Model of Zika Virus Infection.

The 2015/2016 Zika virus epidemic in South and Central America left the scientific community urgently trying to understand the factors that contribute to Zika virus pathogenesis. Because multiple other flaviviruses are endemic in areas where Zika virus emerged, it is hypothesized that a key to understanding Zika virus disease severity is to study Zika virus infection in the context of prior flavivirus exposure. Human and animal studies have highlighted the idea that having been previously exposed to a different flavivirus may modulate the immune response to Zika virus. However, it is still unclear how prior flavivirus exposure impacts Zika viral burden and disease. In this murine study, we longitudinally examine multiple factors involved in Zika disease, linking viral burden with increased neurological disease severity, weight loss, and inflammation. We show that prior heterologous flavivirus exposure with dengue virus type 2 or 3 or the vaccine strain of yellow fever provides protection from mortality in a lethal Zika virus challenge. However, reduction in viral burden and Zika disease varies depending on the infecting primary flavivirus; with primary Zika virus infection being most protective from Zika virus challenge, followed by dengue virus 2, with yellow fever and dengue virus 3 protecting against mortality but showing more severe disease. This study demonstrates the variation in protective effects of prior flavivirus exposure on Zika virus pathogenesis and identifies distinct relationships between primary flavivirus infection and the potential for Zika virus disease. IMPORTANCE The emergence and reemergence of various vector-borne diseases in recent years highlights the need to understand the mechanisms of protection for each pathogen. In this study, we investigated the impact of prior exposure to Zika virus, dengue virus serotypes 2 or 3, or the vaccine strain of yellow fever on pathogenesis and disease outcomes in a mouse model of Zika virus infection. We found that prior exposure to a heterologous flavivirus was protective from mortality, and to varying degrees, prior flavivirus exposure was protective against neurological disease, weight loss, and severe viral burden during a lethal Zika challenge. Using a longitudinal and cross-sectional study design, we were able to link multiple disease parameters, including viral burden, with neurological disease severity, weight loss, and inflammatory response in the context of flavivirus infection. This study demonstrates a measurable but varied impact of prior flavivirus exposure in modulating flavivirus pathophysiology. Given the cyclic nature of most flavivirus outbreaks, this work will contribute to the forecasting of disease severity for future outbreaks.

Vaccination reshapes the virus-specific T cell repertoire in unexposed adults.

We examined how baseline CD4+ T cell repertoire and precursor states impact responses to pathogen infection in humans using primary immunization with yellow fever virus (YFV) vaccine. YFV-specific T cells in unexposed individuals were identified by peptide-MHC tetramer staining and tracked pre- and post-vaccination by tetramers and TCR sequencing. A substantial number of YFV-reactive T cells expressed memory phenotype markers and contained expanded clones in the absence of exposure to YFV. After vaccination, pre-existing YFV-specific T cell populations with low clonal diversity underwent limited expansion, but rare populations with a reservoir of unexpanded TCRs generated robust responses. These altered dynamics reorganized the immunodominance hierarchy and resulted in an overall increase in higher avidity T cells. Thus, instead of further increasing the representation of dominant clones, YFV vaccination recruits rare and more responsive T cells. Our findings illustrate the impact of vaccines in prioritizing T cell responses and reveal repertoire reorganization as a key component of effective vaccination.

Serum biomarker profile orchestrating the seroconversion status of patients with autoimmune diseases upon planned primary 17DD Yellow fever vaccination.

The present study aimed to investigate whether the serum biomarkers of immune response orchestrate the seroconversion status in patients with autoimmune diseases (AID) upon planned primary 17DD-YF vaccination. For this purpose a total of 161 individuals were enrolled in a prospective study, including patients with Rheumatoid Arthritis (RA = 38), Spondyloarthritis (SpA = 51), Systemic Lupus Erythematosus (SLE = 21) and Sjögren's Syndrome (SS = 30) along with a group of healthy controls (HC = 21). Analysis of plaque reduction neutralization test (PRNT) titers and seropositivity rates along with the 17DD-YF viremia and serum biomarkers were carried out at distinct time points (D0/D3-4/D5-6/D7/D14-28). The results demonstrated an overall lower PRNT titer and seropositivity rate (170 vs. 448; 77 vs. 95%) in AID as compared to HC, especially in SpA and SLE subgroups. No significant differences were observed in the viremia levels amongst groups. In general, a more prominent serum biomarker response was observed in AID as compared to HC, throughout the timeline kinetics. Remarkably, AID/PRNT(-) exhibited higher levels of several biomarkers at baseline as compared to AID/PRNT+. Moreover, while AID/PRNT(+) exhibited earlier increase in serum biomarkers at D3-4/D5-6, the AID/PRNT(-) displayed higher response at later time points (D7/D14-D28). Of note, a synchronic increase of IFN-γ at the peak of viremia (D5-6) was observed in HC and AID/PRNT(+) groups, whereas a later asynchronous IFN-γ response was reported for AID/PRNT(-) at D7. The biomarker profile tends to deflate at post-vaccination timeline, highlighting a putative immunomodulatory effect of live attenuated 17DD-YF vaccine in AID/PRNT(+), but not in AID/PRNT(-). Altogether these data suggested that inflammatory status prior vaccination, low IFN-γ at viremia peak and the occurrence of asynchronous biomarker storm after 17DD-YF vaccination may orchestrate the lack of neutralizing antibody response γ.

Immunogenicity and duration of protection after yellow fever vaccine in people living with human immunodeficiency virus: a systematic review.

BACKGROUND: We lack the rationale on which to base the development of a yellow fever (YF) vaccination schedule for people living with human immunodeficiency virus (PLWHIV). OBJECTIVES: To report on the current evidence regarding the seroconversion rate and the duration of humoral protection after YF vaccine, as well as the impact of revaccination in PLWHIV. DATA SOURCES: MEDLINE, Google Scholar, LILACS and Cochrane CENTRAL were searched. METHODS: We selected studies on PLWHIV of all ages (including perinatally HIV-infected patients) and all settings (YF endemic and non-endemic zones). Intervention investigated was vaccination against YF, at least once after the HIV diagnosis. The research questions were the seroconversion rate, duration of humoral immunity after YF vaccine and impact of revaccination in PLWHIV. Selected studies were assessed for quality using the Newcastle-Ottawa scale. RESULTS: Ten, six and six studies were selected for the systematic review of each question, respectively. Only one study addressed the first question in perinatally HIV-infected children. The quality of the studies was assessed as Poor (n = 16), Fair (n = 2) or Good (n = 4). A meta-analysis demonstrated that 97.6% (95% CI 91.6%-100%) of the included population seroconverted. Between 1 and 10 years after YF vaccine, reported persistence of neutralizing antibodies was 72% (95% CI 53.6%-91%), and it was 62% (95% CI 45.4%-78.6%) more than 10 years after YF vaccine. No conclusions could be drawn on impact of revaccination because of the small number of patients. CONCLUSIONS: The current evidence regarding seroconversion rate, duration of humoral protection after YF vaccine and impact of revaccination in PLWHIV is limited by the low number and quality of studies. Based on the presently available data, it is difficult to rationally develop yellow fever vaccination guidelines for PLWHIV.

Pre-existing Immunity to Japanese Encephalitis Virus Alters CD4 T Cell Responses to Zika Virus Inactivated Vaccine.

The epidemic spread of Zika virus (ZIKV), associated with devastating neurologic syndromes, has driven the development of multiple ZIKV vaccines candidates. An effective vaccine should induce ZIKV-specific T cell responses, which are shown to improve the establishment of humoral immunity and contribute to viral clearance. Here we investigated how previous immunization against Japanese encephalitis virus (JEV) and yellow fever virus (YFV) influences T cell responses elicited by a Zika purified-inactivated virus (ZPIV) vaccine. We demonstrate that three doses of ZPIV vaccine elicited robust CD4 T cell responses to ZIKV structural proteins, while ZIKV-specific CD4 T cells in pre-immunized individuals with JEV vaccine, but not YFV vaccine, were more durable and directed predominantly toward conserved epitopes, which elicited Th1 and Th2 cytokine production. In addition, T cell receptor repertoire analysis revealed preferential expansion of cross-reactive clonotypes between JEV and ZIKV, suggesting that pre-existing immunity against JEV may prime the establishment of stronger CD4 T cell responses to ZPIV vaccination. These CD4 T cell responses correlated with titers of ZIKV-neutralizing antibodies in the JEV pre-vaccinated group, but not in flavivirus-naïve or YFV pre-vaccinated individuals, suggesting a stronger contribution of CD4 T cells in the generation of neutralizing antibodies in the context of JEV-ZIKV cross-reactivity.

Assessment of immunity against Yellow Fever virus infections in northeastern Nigeria using three serological assays.

Poor systematic surveillance for Yellow Fever virus (YFV) is primarily due to lack of affordable diagnostic facilities in resource-constrained countries. This study aimed at providing evidence-based information on immunity against Yellow Fever with a view to assessing the possibility of the recent epidemics persisting in Nigeria. Six hundred patients with febrile illness seeking malaria test in selected hospitals were tested for YFV antibody using three serological assays: ELISA IgM, microneutralization test (MNT) and plaque reduction neutralization test (PRNT). The three assays commonly detected YFV antibody (Ab) in 1.7% patients, MNT: IgM in 8.3%, IgM: PRNT in 7.1%, and MNT: PRNT in 3.2%. Immunity against YF was significantly higher in Bauchi and Borno than Adamawa and children aged 0-9 years compared to 20-29 years. YFV neutralizing antibody (nAb) strongly correlated with the vaccination status of the patients. More unvaccinated patients had nAb compared with the vaccinated. Immunity against YF among treated patients with antibiotic and/or antimalaria before sample collection inversely correlated with the untreated. YVnAb among unvaccinated indicates natural infections. Acute YFV infections were mistaken for malaria and natural infections are ongoing. Individuals aged more than or equal to 20 years should be targeted during mass vaccination campaigns. With low population immunity, repetitive YF epidemics in Nigeria is not yet over. The current policy on Yellow Fever vaccination in Nigeria still leaves a large unimmunized population at the risk of epidemics. Sufficient mass vaccination in combination with National Programme on Immunization remains key to averting YF epidemics.

Auto-antibodies to type I IFNs can underlie adverse reactions to yellow fever live attenuated vaccine.

Yellow fever virus (YFV) live attenuated vaccine can, in rare cases, cause life-threatening disease, typically in patients with no previous history of severe viral illness. Autosomal recessive (AR) complete IFNAR1 deficiency was reported in one 12-yr-old patient. Here, we studied seven other previously healthy patients aged 13 to 80 yr with unexplained life-threatening YFV vaccine-associated disease. One 13-yr-old patient had AR complete IFNAR2 deficiency. Three other patients vaccinated at the ages of 47, 57, and 64 yr had high titers of circulating auto-Abs against at least 14 of the 17 individual type I IFNs. These antibodies were recently shown to underlie at least 10% of cases of life-threatening COVID-19 pneumonia. The auto-Abs were neutralizing in vitro, blocking the protective effect of IFN-α2 against YFV vaccine strains. AR IFNAR1 or IFNAR2 deficiency and neutralizing auto-Abs against type I IFNs thus accounted for more than half the cases of life-threatening YFV vaccine-associated disease studied here. Previously healthy subjects could be tested for both predispositions before anti-YFV vaccination.

Vogt-Koyanagi-Harada-like Disease following Yellow Fever Vaccination.

Purpose: To report the manifestation of Vogt-Koyanagi-Harada-like disease (VKH) following yellow fever vaccination.Methods: Case report.Results: A 34-year-old immunocompetent male had tinnitus, headache, and decreased vision after a booster dose of yellow fever vaccine. Visual acuity was 20/100 in the right eye and 20/80 in the left, with serous retinal detachment (SRD) and choroidal thickening identified on clinical examination and multimodal imaging. Lumbar puncture revealed pleocytosis and an increased protein content, but extensive investigations ruled out infectious/neurological diseases. Pulse intravenous methylprednisolone was given, followed by a tapering regimen of high-dose oral prednisone. Azathioprine was started early, 3 weeks after initiation of oral steroids. Intraocular inflammation and SRD rapidly resolved, with visual acuity reaching 20/20 in both eyes, after 3 weeks. No recurrence of intraocular inflammation or sign of depigmentation was so far noticed, at 2 years of follow-up.Conclusion: Yellow fever vaccine may be a possible trigger for VKH.