Evaluation of accuracy and reliability of the plaque reduction neutralization test (micro-PRNT) in detection of yellow fever virus antibodies

Safety and immunogenicity of different 17DD yellow fever vaccines in golden-headed tamarins (Leontopithecus chrysomelas): Inhibition of viremia and RNAemia after homologous live-attenuated vaccination

Yellow fever (YF) is a viral disease that affects both humans and non-human primates (NHPs). Neotropical monkeys are more severely stricken by YF and the impact of the disease can be devastating to the endangered golden-headed lion tamarins (GHLTs, Leontopithecus chrysomelas). Susceptible GHLTs were immunized with the commercial Brazilian YF 17DD live attenuated vaccine or two other experimental non-replicating YF vaccines: a purified whole-virus, b-propiolactone-inactivated vaccine and a plant-derived recombinant subunit vaccine. Safety, immunogenicity and viremia and RNAemia blockade were characterized. No YF clinical manifestations were observed in any of the GHLTs that received the attenuated virus, either as a vaccine or as the homologous vaccination with the live attenuated vaccine used as the challenge virus. All three concentrations of the attenuated vaccine induced neutralizing antibodies and only one in 16 animals had detectable viremia and RNAemia after challenge. The inactivated vaccine elicited neutralizing antibodies preventing post-challenge viremia and RNAemia in five out of six animals. The plant-based vaccine induced neutralizing antibodies in five out of six animals and prevented viremia and RNAemia in three out of six against challenge. The safety profile and the immunogenicity of the YF attenuated vaccine were demonstrated in GHLTs with a blocking effectiveness over 90 %, where blockade can be defined as the capacity to prevent viremia and RNAemia after homologous vaccination with the live attenuated vaccine. The use of the inactivated vaccine in this species served as a preliminary pre-clinical study for this approach and after administration in three-dose regimen demonstrated a blocking profile of 83 %. Using a two-dose regimen, the plant-based vaccine was able to block viremia and RNAemia in 50 % of the animals. The present study can endorse the use of attenuated or non-replicating yellow fever vaccines in New World primates threatened by the recent disease outbreaks in Brazil.

Hydroxychloroquine is associated with lower seroconversion upon 17DD-Yellow fever primovaccination in patients with primary Sjögren's syndrome

The present study aimed at investigating whether the hydroxychloroquine (HCQ) treatment would impact the neutralizing antibody production, viremia levels and the kinetics of serum soluble mediators upon planned 17DD-Yellow Fever (YF) primovaccination (Bio-Manguinhos-FIOCRUZ) of primary Sjögren's syndrome (pSS). A total of 34 pSS patients and 23 healthy controls (HC) were enrolled. The pSS group was further categorized according to the use of HCQ (HCQ and Non-HCQ). The YF-plaque reduction neutralization test (PRNT ≥1:50), YF viremia (RNAnemia) and serum biomarkers analyses were performed at baseline and subsequent time-points (Day0/Day3-4/Day5-6/Day7/Day14-D28). The pSS group showed PRNT titers and seropositivity rates similar to those observed for HC (GeoMean = 238 vs 440, p = .11; 82% vs 96%, p = .13). However, the HCQ subgroup exhibited lower seroconversion rates as compared to HC (GeoMean = 161 vs 440, p = .04; 69% vs 96%, p = .02) and Non-HQC (GeoMean = 161 vs 337, p = .582; 69% vs 94%, p = .049). No differences in YF viremia were observed amongst subgroups. Serum biomarkers analyses demonstrated that HCQ subgroup exhibited increased levels of CCL2, CXL10, IL-6, IFN-γ, IL1-Ra, IL-9, IL-10, and IL-2 at baseline and displayed a consistent increase of several biomarkers along the kinetics timeline up to D14-28. These results indicated that HCQ subgroup exhibited a deficiency in assembling YF-specific immune response elicited by 17DD-YF primovaccination as compared to Non-HCQ subgroup. Our findings suggested that hydroxychloroquine is associated with a decrease in the humoral immune response after 17DD-YF primovaccination.

First DFT-supported point of care and novel electrochemical biosensing: Determination of yellow fever NS1 antibody in human plasma

In our study, we developed a point of care electrochemical biosensing platform based on the functionalized cysteine-positioned gold electrode to diagnose yellow fever disease from human plasma samples. The developed platform underwent characterization through diverse methods encompassing cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and density-functional theory. The capacitive interaction between yellow fever virus non-structural antigen and antibody gave a cathodic signal at approximately -260 mV, and increased in proportion to the amount of non-structural antibody. The created electrochemical biosensor has an ability to detect 96 ag/mL of the yellow fever non-structural antibody with an extensive analytical range varied from 0.1 fg/mL to 1 μg/mL. The interference effects of various substances that could be found in human plasma, and the performance of the method were examined from the point of recovery and relative standard deviation for human plasma samples; hereby, the results confirmed the unprecedented selectivity and accuracy of the proposed method.

Impact of HIV-Related Immune Impairment of Yellow Fever Vaccine Immunogenicity in People Living with HIV-ANRS 12403

The yellow fever (YF) vaccine is one of the safest and most effective vaccines currently available. Still, its administration in people living with HIV (PLWH) is limited due to safety concerns and a lack of consensus regarding decreased immunogenicity and long-lasting protection for this population. The mechanisms associated with impaired YF vaccine immunogenicity in PLWH are not fully understood, but the general immune deregulation during HIV infection may play an important role. To assess if HIV infection impacts YF vaccine immunogenicity and if markers of immune deregulation could predict lower immunogenicity, we evaluated the association of YF neutralization antibody (NAb) titers with the pre-vaccination frequency of activated and exhausted T cells, levels of pro-inflammatory cytokines, and frequency of T cells, B cells, and monocyte subsets in PLWH and HIV-negative controls. We observed impaired YF vaccine immunogenicity in PLWH with lower titers of YF-NAbs 30 days after vaccination, mainly in individuals with CD4 count <350 cells/mm3. At the baseline, those individuals were characterized by having a higher frequency of activated and exhausted T cells and tissue-like memory B cells. Elevated levels of those markers were also observed in individuals with CD4 count between 500 and 350 cells/mm3. We observed a negative correlation between the pre-vaccination level of CD8+ T cell exhaustion and CD4+ T cell activation with YF-NAb titers at D365 and the pre-vaccination level of IP-10 with YF-NAb titers at D30 and D365. Our results emphasize the impact of immune activation, exhaustion, and inflammation in YF vaccine immunogenicity in PLWH.

Yellow fever neutralizing antibody seroprevalence proportion and titers in previously vaccinated adults with chronic kidney disease

Studies on yellow fever vaccine (YF) in chronic kidney disease (CKD) patients are scarce. This cross-sectional study aimed to evaluate YF neutralizing antibody seroprevalence and titers in previously vaccinated adults with CKD, on dialysis (D-CKD) or not (ND-CKD), compared to healthy persons. The micro Plaque Reduction Neutralization-Horseradish Peroxidase (μPRN-HP) test was used. Antibody titers were expressed as the reciprocal of the highest dilution that neutralized the challenge virus by 50 % (μPRN50). Seropositivity cut-off was set at ≥ 1:100. We included 153 participants: 46 ND-CKD, 50 D-CKD and 57 healthy adults. Median ages were 58.3, 55 and 52.2 years, respectively. Median time since YF vaccination was 22.3, 18.5 and 48.3 months respectively. There were no statistically significant differences in YF seroprevalence and neutralizing antibodies titers among groups: 100 % of ND-CKD; 96 % of D-CKD and 100 % of healthy participants were seropositive. Geometric mean titers (GMT) were 818.5, 683.0 and 665.5, respectively (p = 0.289).

Comprehensive landscape of neutralizing antibody and cell-mediated response elicited by the 1/5 fractional dose of 17DD-YF primary vaccination in adults

The present study aimed at evaluating the YF-specific neutralizing antibody profile besides a multiparametric analysis of phenotypic/functional features of cell-mediated response elicited by the 1/5 fractional dose of 17DD-YF vaccine, administered as a single subcutaneous injection. The immunological parameters of each volunteer was monitored at two time points, referred as: before (Day 0) [Non-Vaccinated, NV(D0)] and after vaccination (Day 30-45) [Primary Vaccinees, PV(D30-45)]. Data demonstrated high levels of neutralizing antibodies for PV(D30-45) leading to a seropositivity rate of 93%. A broad increase of systemic soluble mediators with a mixed profile was also observed for PV(D30-45), with IFN-γ and TNF-α presenting the highest baseline fold changes. Integrative network mapping of soluble mediators showed increased correlation numbers in PV(D30-45) as compared to NV(D0) (532vs398). Moreover, PV(D30-45) exhibited increased levels of Terminal Effector (CD45RA+CCR7-) CD4+ and CD8+ T-cells and Non-Classical memory B-cells (IgD+CD27+). Dimensionality reduction of Mass Cytometry data further support these findings. A polyfunctional cytokine profile (TNF-α/IFN-γ/IL-10/IL-17/IL-2) of T and B-cells was observed upon in vitro antigen recall. Mapping and kinetics timeline of soluble mediator signatures for PV(D30-45) further confirmed the polyfunctional profile upon long-term in vitro culture, mediated by increased levels of IFN-γ and TNF-α along with decreased production of IL-10. These findings suggest novel insights of correlates of protection elicited by the 1/5 fractional dose of 17DD-YF vaccine.

Safety of the yellow fever vaccine in people living with HIV: a longitudinal study exploring post-vaccination viremia and hematological and liver kinetics

BACKGROUND

Safety data on the yellow fever vaccine 17DD in People Living with HIV (PLWH) are limited. This study explored the occurrence of post-vaccination 17DD viremia and the kinetics of hematological and liver laboratorial parameters in PLWH and HIV-uninfected participants [HIV(-) controls].

METHODS

We conducted a secondary analysis of a longitudinal interventional trial (NCT03132311) study that enrolled PLWH and HIV(-) controls to receive a single 17DD dose and were followed at 5, 30 and 365 days after vaccination in Rio de Janeiro, Brazil. 17DD viremia (obtained throughreal-time PCR and plaque forming units' assays), hematological (neutrophils, lymphocytes and platelets counts) and liver enzymes (ALT and AST) results were assessed at baseline and Days 5 and 30 post-vaccination. Logistic regression models explored factors associated with the odds of having positive 17DD viremia. Linear regression models explored variables associated with hematological and liver enzymes results at Day 5.

RESULTS

A total of 202 PLWH with CD4 ≥ 200 cells/µL and 68 HIV(-) controls were included in the analyses. 17DD viremia was found in 20.0 % of the participants and was twice more frequent in PLWH than in HIV(-) controls (22.8% vs. 11.8 %, p-value < 0.001). Neutrophils, lymphocytes and platelets counts dropped at Day 5 and returned to baseline values at Day 30. 17DD viremia was associated with lower nadir of lymphocytes and platelets at Day 5. ALT levels did not increase post-vaccination and were not associated with 17DD viremia.

CONCLUSIONS

17DD was safe and well-tolerated in PLWH with CD4 ≥ 200 cells/µL. Post-vaccination viremia was more frequent in PLWH than in controls. Transient and self-limited decreases in lymphocytes and neutrophils occurred early after vaccination. 17DD viremia was associated with lower lymphocytes and platelets nadir after vaccination. We did not observe elevations in ALT after 17DD vaccination.

Serological investigation of vaccine-induced antibodies for measles, rubella, and yellow fever viruses in children vertically exposed to Zika virus or with down syndrome

Background

Vaccination schedules, as well as their effectiveness and contraindications, need to be evaluated regularly, especially in specific situations. Congenital Zika Syndrome (CZS) is a severe condition that results in extensive functional and neurological impairment of fetuses and newborns due to Zika virus tropism for fetal neural progenitor cells. Down Syndrome (DS) is the leading genetic cause of intellectual disability. The immune impairment in DS has already been described, but little is known about the immune response of CZS children. Thus, CZS and DS are specific conditions that can be considered for a reassessment of the available immunizations. Here, we carried out serological analyses of attenuated vaccines-induced antibodies for measles, rubella, and yellow fever viruses in children aged 2-7, grouped into asymptomatic controls, DS children, and CZS children.

Methods

Plasma samples were taken, and vaccination records were compiled during clinical follow-up. Enzymatic immunoassays for quantifying anti-measles and anti-rubella IgG were performed to assess the response to the Measles, Mumps, and Rubella (MMR) vaccine. Plaque Reduction Neutralization Test (PRNT) was performed to investigate neutralizing antibodies in response to the Brazilian vaccine strain of yellow fever (YF-17DD).

Results

We highlight similar levels of anti-measles IgG and neutralizing antibodies for YF-17DD among CZS, DS, and asymptomatic children, although low positivity of measles data was seen in the three groups. In DS children, the 2-4-year-old group had an increased level of anti-measles IgG compared to the older group of children aged five to seven years. Lower anti-rubella IgG levels were observed in CZS and DS children compared to asymptomatic children. For anti-rubella IgG, the good performance of vaccination in asymptomatic children is due to younger ones rather than older ones.

Conclusions

There were no reports of adverse events after the use of the MMR and YF-17DD indicating that CZS and DS could continue to receive these vaccines, but our data draws attention to the necessity of monitoring the vaccination response in CZS and DS children over time and the possible need to adhere to national measles vaccination campaigns. Scientific research needs to continue to help develop appropriate CZS and DS health guidelines.

Immunogenicity and reactogenicity of yellow fever vaccine in people with HIV

OBJECTIVE

To evaluate immunogenicity and reactogenicity of yellow fever (YF) vaccine in people with HIV (PWH) compared to HIV-uninfected controls.

DESIGN

In this longitudinal interventional trial (NCT03132311), PWH with CD4 + cell count ≥200 cells/μl and controls, aged 18-59, without a previous history of YF vaccination received a single standard dose of YF vaccine (17DD) and were followed at Days 5, 30 and Year 1.

METHODS

YF-neutralization titers were measured at Days 0, 30 and Year 1 and geometric mean titers (GMT) were calculated. Adverse events (AE) and YF virus detection were measured at Days 5 and 30. Linear regression evaluated factors associated with YF-neutralization titers.

RESULTS

Two hundred and eighteen PWH and 82 controls were included. At baseline, all PWH were using antiretroviral therapy; 92.6% had undetectable HIV viral load (VL) and median CD4 + cell count was 630 cells/μl [interquartile range (IQR) 463-888]. YF vaccine was safe and there were no serious AEs. At Day 30, seroconversion was observed in 98.6% of PWH [95% confidence interval (CI): 95.6-99.6] and in 100% of controls (95% CI: 93.9-100); at Year 1, 94.0% of PWH (95% CI: 89.6-96.7) and 98.4% of controls (95% CI 90.3-99.9) were seropositive. PWH had lower GMTs than controls at Day 30 and Year 1. Baseline VL >1000 copies/ml, low CD4 + cell count and low CD4 + /CD8 + ratio were associated with lower YF-neutralization titers.

CONCLUSIONS

YF vaccine is safe in PWH with CD4 + cell count ≥200 cells/μl. YF vaccine immunogenicity is impaired in PWH, particularly among those with high VL, low CD4 + cell count and low CD4 + /CD8 + ratio at vaccination and YF-neutralization titers decays over time.

Enhancing Inactivated Yellow Fever 17D Vaccine-Induced Immune Responses in Balb/C Mice Using Alum/CpG

There are some concerns about the safety of live attenuated yellow fever vaccines (YF-live), particularly viscerotropic adverse events, which have a high mortality rate. The cellular production of the vaccine will not cause these adverse effects and has the potential to extend applicability to those who have allergic reactions, immunosuppression, and age. In this study, inactivated yellow fever (YF) was prepared and adsorbed with Alum/CpG. The cellular and humoral immunities were investigated in a mouse model. The results showed that Alum/CpG (20 μg/mL) could significantly increase the binding and neutralizing activities of the antibodies against YF. Moreover, the antibody level at day 28 after one dose was similar to that of the attenuated vaccine, but significantly higher after two doses. At the same time, Alum/CpG significantly increased the levels of IFN-γ and IL-4 cytokines.

Immunogenicity and safety of fractional doses of 17D-213 yellow fever vaccine in HIV-infected people in Kenya (YEFE): a randomised, double-blind, non-inferiority substudy of a phase 4 trial

BACKGROUND

Evidence indicates that fractional doses of yellow fever vaccine are safe and sufficiently immunogenic for use during yellow fever outbreaks. However, there are no data on the generalisability of this observation to populations living with HIV. Therefore, we aimed to evaluate the immunogenicity of fractional and standard doses of yellow fever vaccine in HIV-positive adults.

METHODS

We conducted a randomised, double-blind, non-inferiority substudy in Kilifi, coastal Kenya to compare the immunogenicity and safety of a fractional dose (one-fifth of the standard dose) versus the standard dose of 17D-213 yellow fever vaccine among HIV-positive volunteers. HIV-positive participants aged 18-59 years, with baseline CD4+ T-cell count of at least 200 cells per mL, and who were not pregnant, had no previous history of yellow fever vaccination or infection, and had no contraindication for yellow fever vaccination were recruited from the community. Participants were randomly assigned 1:1 in blocks (variable block sizes) to either a fractional dose or a standard dose of the 17D-213 yellow fever vaccine. Vaccines were administered subcutaneously by an unblinded nurse and pharmacist; all other study personnel were blinded to the vaccine allocation. The primary outcome of the study was the proportion of participants who seroconverted by the plaque reduction neutralisation test (PRNT50) 28 days after vaccination for the fractional dose versus the standard dose in the per-protocol population. Secondary outcomes were assessment of adverse events and immunogenicity during the 1-year follow-up period. Participants were considered to have seroconverted if the post-vaccination antibody titre was at least 4 times greater than the pre-vaccination titre. We set a non-inferiority margin of not less than a 17% decrease in seroconversion in the fractional dose compared with the standard dose. This study is registered with ClinicalTrials.gov, NCT02991495.

FINDINGS

Between Jan 29, 2019, and May 17, 2019, 303 participants were screened, and 250 participants were included and vaccinated; 126 participants were assigned to the fractional dose and 124 to the standard dose. 28 days after vaccination, 112 (96%, 95% CI 90-99) of 117 participants in the fractional dose group and 115 (98%, 94-100) of 117 in the standard dose group seroconverted by PRNT50. The difference in seroconversion between the fractional dose and the standard dose was -3% (95% CI -7 to 2). Fractional dosing therefore met the non-inferiority criterion, and non-inferiority was maintained for 1 year. The most common adverse events were headache (n=31 [12%]), fatigue (n=23 [9%]), myalgia (n=23 [9%]), and cough (n=14 [6%]). Reported adverse events were either mild (182 [97%] of 187 adverse events) or moderate (5 [3%]) and were self-limiting.

INTERPRETATION

Fractional doses of the 17D-213 yellow fever vaccine were sufficiently immunogenic and safe demonstrating non-inferiority to the standard vaccine dose in HIV-infected individuals with CD4+ T cell counts of at least 200 cells per mL. These results provide confidence that fractional dose recommendations are applicable to populations with high HIV prevalence.

FUNDING

Wellcome Trust, Médecins Sans Frontières Foundation, and the UK Department for International Development.

Immuno-Colorimetric Neutralization Test: A Surrogate for Widely Used Plaque Reduction Neutralization Tests in Public Health Virology

Since their first documentation in 1952, plaque reduction neutralization tests (PRNTs) have become the choice of test for the measurement of neutralizing antibodies against a particular virus. However, PRNTs can be performed only against viruses that cause cytopathic effects (CPE). PRNTs also require skilled personnel and can be time-consuming depending on the time required for the virus to cause CPE. Hence, their application limits large-scale studies or epidemiological and laboratory investigations. Since 1978, many surrogate PRNTs or immunocolorimetric assay (ICA)-based focus reduction neutralization tests (FRNT) have been developed. In this article, ICAs and their utility in FRNTs for the characterization of neutralizing antibodies, homologous or heterologous cross-neutralization, and laboratory diagnosis of viruses of public health importance have been discussed. Additionally, possible advancements and automations have been described that may help in the development and validation of novel surrogate tests for emerging viruses.

Development of an optical sandwich ELONA using a pair of DNA aptamers for yellow fever virus NS1

Here, we proposed an enzyme-linked oligonucleotide assay (ELONA) for yellow fever (YF) diagnosis that uses a pair of aptamers, YFns1-4 and YFns1-31. The aptamers were selected to specifically bind to nonstructural protein 1 (NS1), which is secreted at a high concentration after YF infection. We applied the aptamers which did not interfere with each other on binding to the NS1 in a sandwich ELONA. In the assay, the best detection sensitivity was obtained when the combination of YFns1-31 as a capture aptamer and YFns1-4 as a detect aptamer was used. The sensitivity could be attributed to the results of the direct ELONA with each YFns1-4 and YFns1-31; a great absorbance intensity and a broad detectable range of NS1, respectively. The sandwich ELONA achieved a low detection limit of 0.85 nM in buffer and was highly specific to the YFV-NS1 as its detection signals were significantly distinct from those of other flavivirus-derived NS1. In addition, the assay showed a desirable sensitivity in serum-spiked condition. Our developed sandwich ELONA can be a new practical and applicable serological diagnostics in YF endemic regions where other flaviviruses coexist and facilities for complex diagnostic tests are lacking.

Serosurvey in Two Dengue Hyperendemic Areas of Costa Rica Evidence Active Circulation of WNV and SLEV in Peri-Domestic and Domestic Animals and in Humans

Costa Rica harbors several flaviviruses, including Dengue (DENV), Zika (ZIKV), West Nile virus (WNV), and Saint Louis encephalitis virus (SLEV). While DENV and ZIKV are hyperendemic, previous research indicates restricted circulation of SLEV and WNV in animals. SLEV and WNV seroprevalence and high transmission areas have not yet been measured. To determine the extents of putative WNV and SLEV circulation, we sampled peri-domestic and domestic animals, humans, and mosquitoes in rural households located in two DENV and ZIKV hyperendemic regions during the rainy and dry seasons of 2017-2018 and conducted plaque reduction neutralization test assay for serology (PRNT) and RT-PCR for virus detection. In Cuajiniquil, serological evidence of WNV and SLEV was found in equines, humans, chickens, and wild birds. Additionally, five seroconversion events were recorded for WNV (2 equines), SLEV (1 human), and DENV-1 (2 humans). In Talamanca, WNV was not found, but serological evidence of SLEV circulation was recorded in equines, humans, and wild birds. Even though no active viral infection was detected, the seroconversion events recorded here indicate recent circulation of SLEV and WNV in these two regions. This study thus provides clear-cut evidence for WNV and SLEV presence in these areas, and therefore, they should be considered in arboviruses differential diagnostics and future infection prevention campaigns.

A High-Throughput Yellow Fever Neutralization Assay

Quick and accurate detection of neutralizing antibodies (nAbs) against yellow fever is essential in serodiagnosis during outbreaks for surveillance and to evaluate vaccine efficacy in population-wide studies. All of this requires serological assays that can process a large number of samples in a highly standardized format. Albeit being laborious, time-consuming, and limited in throughput, the classical plaque reduction neutralization test (PRNT) is still considered the gold standard for the detection and quantification of nAbs due to its sensitivity and specificity. Here, we report the development of an alternative fluorescence-based serological assay (SNTFLUO) with an equally high sensitivity and specificity that is fit for high-throughput testing with the potential for automation. Finally, our novel SNTFLUO was cross-validated in several reference laboratories and against international WHO standards, showing its potential to be implemented in clinical use. SNTFLUO assays with similar performance are available for the Japanese encephalitis, Zika, and dengue viruses amenable to differential diagnostics. IMPORTANCE Fast and accurate detection of neutralizing antibodies (nAbs) against yellow fever virus (YFV) is key in yellow fever serodiagnosis, outbreak surveillance, and monitoring of vaccine efficacy. Although classical PRNT remains the gold standard for measuring YFV nAbs, this methodology suffers from inherent limitations such as low throughput and overall high labor intensity. We present a novel fluorescence-based serum neutralization test (SNTFLUO) with equally high sensitivity and specificity that is fit for processing a large number of samples in a highly standardized manner and has the potential to be implemented for clinical use. In addition, we present SNTFLUO assays with similar performance for Japanese encephalitis, Zika, and dengue viruses, opening new avenues for differential diagnostics.

Previous biological therapy and impairment of the IFN-γ/IL-10 axis are associated with low immune response to 17DD-YF vaccination in patients with spondyloarthritis

Yellow fever (YF) vaccination is known to induce a suboptimal response in patients with autoimmune diseases (AIDs). To date, few studies have focused on the performance of 17DD-YF vaccination in patients with spondyloarthritis (SpA). In general, patients with SpA are young and have less comorbidities than other patients with AIDs, and frequently receive biological disease-modifying antirheumatic drugs (DMARDs) that may impact their response to vaccines. Taking this background information, the present study aimed to investigate whether the use of biological DMARDs, even after planned washout, or disease activity measured by the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), would impact the overall performance of planned 17DD-YF primary vaccination in patients with SpA. For this purpose, 74 subjects were enrolled in a prospective study, including adult patients with SpA (SpA; n = 51) and a healthy control (HC; n = 23) group. Analysis of YF specific neutralizing antibodies test (PRNT), along with YF viremia and the levels of serum chemokines, cytokines, and growth factors were performed at distinct time points (D0, D3, D4, D5, D6, D7, D14, and D28). The BASDAI scores were evaluated at D0 and D180. Data demonstrated that overall, the SpA group presented lower PRNT titers and seropositivity rates as compared to the HC group (GeoMean = 112 vs. 440; 73% vs. 96%, respectively). In SpA subgroup analyses, previous biological DMARDs (BIO-IT) led to a lower PRNT titers (BIO-IT 79, 95% CI [39-150] vs. without biological DMARDs [non-BIO-IT] 159, 95% CI [94-267], p < 0.001). The non-BIO-IT group achieved a response similar to the HC group (81% vs. 96%, p = 0.112), whereas the BIO-IT group had a lower seroconversion rate (64% vs. 96% HC, p = 0.007). The BASDAI was not associated with PRNT levels and did not change after 6 months of follow-up. No differences in YF viremia were observed amongst subgroups. Higher baseline levels of serum biomarkers were observed in the BIO-IT group vs. the non-BIO-IT group, as well as in those with a BASDAI ≥ 4 vs. those with a BASDAI < 4. Increasing levels of several biomarkers were observed in SpA, especially in the BIO-IT and BASDAI ≥ 4 subgroups throughout the timeline kinetics, with impairment/disturbance in the IFN-γ/IL-10 axis around the peak of viremia (D5). Altogether, these findings suggested that the use of biological DMARDs impacts the response to the 17DD-YF vaccine, even after planned washout. Therefore, previous biological DMARD therapy, the inflammatory status prior vaccination, and impairment of the IFN-γ/IL-10 axis at the peak of viremia may determine the immunogenicity of 17DD-YF vaccination in patients with SpA.

Yellow fever vaccination in Brazil: Short-term safety and immunogenicity in juvenile autoimmune rheumatic diseases

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We examined 17DD yellow fever vaccine in juvenile autoimmune rheumatic disease patients under low immunosuppression during the recent epidemic in Sao Paulo-Brazil.

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No serious adverse events were reported and frequencies of mild adverse events were comparable between patients and healthy controls.

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Immunogenicity parameters against yellow fever vaccine were not hampered in juvenile autoimmune rheumatic disease patients.

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Peripheral white-blood-cells kinetics after yellow fever vaccination was demonstrated with transient decreases in lymphocytes at D5 and neutrophil levels at D10 with complete recovery at D30.

Yellow fever vaccine (YFV) is a live attenuated vaccine usually contraindicated for juvenile autoimmune rheumatic disease (JARD) patients. During the recent epidemic in Sao Paulo-Brazil, YFV was indicated for patients under low immunosuppression. Thirty JARD patients with inactive diseases undergoing low immunosuppression and 30 healthy controls (HC) were vaccinated with a fractional dose 17DD YFV (∼5495 IU) and evaluated 30 days later. JARD patients and controls had comparable median age (12.4 vs. 12 years, p = 0.250). Disease parameters remained stable 30 days after 17DD YFV (p > 0.05) and only mild adverse events were reported in both groups (p > 0.05). JARD and HC had similar seroprotection [93% vs. 100%;p = 0.49], seroconversion rates [96% vs. 100%;p = 0.489], and GMT [1249 vs.1293;p = 0.821]. Both groups had similar white-blood-cells kinetics with transient decreases in lymphocytes at D5 and neutrophils at D10, followed by full recovery at D30 (P < 0.05). In conclusion, 17DD YFV was safe and immunogenic in JARD. This study may contribute to recommendations for patients living/travelling to endemic areas.

Immunogenicity and safety of primary fractional-dose yellow fever vaccine in autoimmune rheumatic diseases

Background

Brazil faced a yellow fever(YF) outbreak in 2016–2018 and vaccination was considered for autoimmune rheumatic disease patients(ARD) with low immunosuppression due to YF high mortality.

Objective

This study aimed to evaluate, prospectively for the first time, the short-term immunogenicity of the fractional YF vaccine(YFV) immunization in ARD patients with low immunossupression.

Methods and Results

A total of 318 participants(159 ARD and 159 age- and sex-matched healthy controls) were vaccinated with the fractional-dose(one fifth) of 17DD-YFV. All subjects were evaluated at entry(D0), D5, D10, and D30 post-vaccination for clinical/laboratory and disease activity parameters for ARD patients. Post-vaccination seroconversion rate(83.7%vs.96.6%, p = 0.0006) and geometric mean titers(GMT) of neutralizing antibodies[1143.7 (95%CI 1012.3–1292.2) vs.731 (95%CI 593.6–900.2), p<0.001] were significantly lower in ARD compared to controls. A lower positivity rate of viremia was also identified for ARD patients compared to controls at D5 (53%vs.70%, p = 0.005) and the levels persisted in D10 for patients and reduced for controls(51%vs.19%, p = 0.0001). The viremia was the only variable associated with seroconvertion. No serious adverse events were reported. ARD disease activity parameters remained stable at D30(p>0.05).

Conclusion

Fractional-dose 17DD-YF vaccine in ARD patients resulted in a high rate of seroconversion rate(>80%) but lower than controls, with a longer but less intense viremia. This vaccine was immunogenic, safe and did not induce flares in ARD under low immunosuppression and may be indicated in YF outbreak situations and for patients who live or travel to endemic areas.

Trial registration

This clinical trial was registered with Clinicaltrials.gov (#NCT03430388).

Yellow fever is a viral hemorragic fever with high mortality rate and the vaccine is a remarkably successful way of preventing it. As a live attenuated virus vaccine, it is not recommended for rheumatic and other immunossupressed patients in general. However, in an outbreak scenario, the risk of dying of the disease can be higher than the risk of a vaccine serious adverse event. In 2018, the fractional-dose yellow fever vaccine was offered to the hospital employees and to the rheumatic patients without or with low immunossupression therapy in Hospital das Clinicas of University of São Paulo, during the yellow fever outbreak in São Paulo, Brazil. In order to optimize the yellow fever vaccine (YFV) supply, the fractional-dose (corresponding to one fifth) was adopted in the public vaccine campaign.

This is the first study evaluating the primary vaccination with fractional-dose YFV in autoimmune rheumatic diseases(ARD) patients (n = 159) under low immunosuppression. Most vaccinated participants were able to produce enough neutralizing antibodies to be protected against yellow fever (seroconversion rate of 84% versus 96% in healthy controls). Neither activity of the rheumatic disease or serious adverse event was identified during the 30 days of followup after the vaccination.

Serosurvey of Nonhuman Primates in Costa Rica at the Human-Wildlife Interface Reveals High Exposure to Flaviviruses

Simple Summary

The presence of flavivirus-specific antibodies in neotropical non-human primates (NPs) (i.e., dengue virus) is well known. However, it is unclear if dengue virus or other flaviviruses could be maintained in sylvatic cycles. We detected the presence of antibodies against dengue virus (DENV-1, DENV-2), Saint Louis encephalitis virus (SLEV), West Nile virus (WNV), and several undetermined flaviviruses in NPs in Costa Rica. Our work suggests continuous exposure of NPs to several flaviviruses in Costa Rica. These findings open the question of whether bidirectional transmission between humans and non-human primates can occur due to human encroachment into NP habitats, the movement of NP into urban settings, or bridging vectors.

Abstract

Arthropod-borne viruses belonging to the flavivirus genus possess an enormous relevance in public health. Neotropical non-human primates (NPs) have been proposed to be susceptible to flavivirus infections due to their arboreal and diurnal habits, their genetic similarity to humans, and their relative closeness to humans. However, the only known flavivirus in the American continent maintained by sylvatic cycles involving NPs is yellow fever virus (YFV), and NPs’ role as potential hosts of other flaviviruses is still unknown. Here, we examined flavivirus exposure in 86 serum samples including 83.7% samples from free-range and 16.3% from captive NPs living in flavivirus-endemic regions of Costa Rica. Serum samples were opportunistically collected throughout Costa Rica in 2000–2015. We used a highly specific micro-plaque reduction neutralization test (micro-PRNT) to determine the presence of antibodies against YFV, dengue virus 1–4 (DENV), Zika virus, West Nile virus (WNV), and Saint Louis encephalitis virus (SLEV). We found evidence of seropositive NPs with homotypic reactivity to SLEV 11.6% (10/86), DENV 10.5% (9/86), and WNV 2.3% (2/86). Heterotypic reactivity was determined in 3.5% (3/86) of individuals against DENV, 1.2% (1/86) against SLEV, and 1.2% (1/86) against WNV. We found that 13.9% (12/86) of NPs were positive for an undetermined flavivirus species. No antibodies against DENV-3, DENV-4, YFV, or ZIKV were found. This work provides compelling serological evidence of flavivirus exposure in Costa Rican NPs, in particular to DENV, SLEV, and WNV. The range of years of sampling and the region from where positives were detected coincide with those in which peaks of DENV in human populations were registered, suggesting bidirectional exposure due to human–wildlife contact or bridging vectors. Our work suggests the continuous exposure of wildlife populations to various flaviviruses of public health importance and underscores the necessity of further surveillance of flaviviruses at the human–wildlife interface in Central America.

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.

Yellow fever virus vaccination: an emblematic model to elucidate robust human immune responses

By preventing infectious diseases, vaccines contribute substantially to public health. Besides, they offer great opportunities to investigate human immune responses. This is particularly true for live-attenuated virus vaccines which cause resolving acute infections and induce robust immunity. The fact that one can precisely schedule the time-point of vaccination enables complete characterization of the immune response over time, short-term and over many years. The live-attenuated Yellow Fever virus vaccine strain YF-17D was developed in the 1930's and gave rise to the 17D-204 and 17DD vaccine sub-strains, administered to over 600 million individuals worldwide. YF vaccination causes a systemic viral infection, which induces neutralizing antibodies that last for a lifetime. It also induces a strong T cell response resembling the ones of acute infections, in contrast to most other vaccines. In spite of its use since 1937, learning how YF vaccination stimulates such strong and persistent immune responses has gained substantial knowledge only in the last decades. Here we summarize the current state of knowledge on the immune response to YF vaccination, and discuss its contribution as a human model to address complex questions on optimal immune responses.

Quantification of SARS-CoV-2 neutralizing antibody by wild-type plaque reduction neutralization, microneutralization and pseudotyped virus neutralization assays

Virus neutralization assays measure neutralizing antibodies in serum and plasma, and the plaque reduction neutralization test (PRNT) is considered the gold standard for measuring levels of these antibodies for many viral diseases. We have developed procedures for the standard PRNT, microneutralization assay (MNA) and pseudotyped virus neutralization assay (PNA) for severe acute respiratory syndrome coronavirus 2. The MNA offers advantages over the PRNT by reducing assay time, allowing increased throughput and reducing operator workload while remaining dependent upon the use of wild-type virus. This ensures that all severe acute respiratory syndrome coronavirus 2 antigens are present, but Biosafety Level 3 facilities are required. In addition to the advantages of MNA, PNA can be performed with lower biocontainment (Biosafety Level 2 facilities) and allows for further increases in throughput. For each new vaccine, it is critical to ensure good correlation of the neutralizing activity measured using PNA against the PRNT or MNA. These assays have been used in the development and licensure of the ChAdOx1 nCoV-19 (AstraZeneca; Oxford University) and Ad26.COV2.S (Janssen) coronavirus disease 2019 vaccines and are critical for demonstrating bioequivalence of future vaccines.

Co-circulation and misdiagnosis led to underestimation of the 2015-2017 Zika epidemic in the Americas

During the 2015-2017 Zika epidemic, dengue and chikungunya-two other viral diseases with the same vector as Zika-were also in circulation. Clinical presentation of these diseases can vary from person to person in terms of symptoms and severity, making it difficult to differentially diagnose them. Under these circumstances, it is possible that numerous cases of Zika could have been misdiagnosed as dengue or chikungunya, or vice versa. Given the importance of surveillance data for informing epidemiological analyses, our aim was to quantify the potential extent of misdiagnosis during this epidemic. Using basic principles of probability and empirical estimates of diagnostic sensitivity and specificity, we generated revised estimates of reported cases of Zika that accounted for the accuracy of diagnoses made on the basis of clinical presentation with or without laboratory confirmation. Applying this method to weekly reported case data from 43 countries throughout Latin America and the Caribbean, we estimated that 944,700 (95% CrI: 884,900-996,400) Zika cases occurred when assuming all confirmed cases were diagnosed using molecular methods versus 608,400 (95% CrI: 442,000-821,800) Zika cases that occurred when assuming all confirmed cases were diagnosed using serological methods. Our results imply that misdiagnosis was more common in countries with proportionally higher reported cases of dengue and chikungunya, such as Brazil. Given that Zika, dengue, and chikungunya appear likely to co-circulate in the Americas and elsewhere for years to come, our methodology has the potential to enhance the interpretation of passive surveillance data for these diseases going forward. Likewise, our methodology could also be used to help resolve transmission dynamics of other co-circulating diseases with similarities in symptomatology and potential for misdiagnosis.

Validation of a yellow fever vaccine model using data from primary vaccination in children and adults, re-vaccination and dose-response in adults and studies with immunocompromised individuals

BACKGROUND

An effective yellow fever (YF) vaccine has been available since 1937. Nevertheless, questions regarding its use remain poorly understood, such as the ideal dose to confer immunity against the disease, the need for a booster dose, the optimal immunisation schedule for immunocompetent, immunosuppressed, and pediatric populations, among other issues. This work aims to demonstrate that computational tools can be used to simulate different scenarios regarding YF vaccination and the immune response of individuals to this vaccine, thus assisting the response of some of these open questions.

RESULTS

This work presents the computational results obtained by a mathematical model of the human immune response to vaccination against YF. Five scenarios were simulated: primovaccination in adults and children, booster dose in adult individuals, vaccination of individuals with autoimmune diseases under immunomodulatory therapy, and the immune response to different vaccine doses. Where data were available, the model was able to quantitatively replicate the levels of antibodies obtained experimentally. In addition, for those scenarios where data were not available, it was possible to qualitatively reproduce the immune response behaviours described in the literature.

CONCLUSIONS

Our simulations show that the minimum dose to confer immunity against YF is half of the reference dose. The results also suggest that immunological immaturity in children limits the induction and persistence of long-lived plasma cells are related to the antibody decay observed experimentally. Finally, the decay observed in the antibody level after ten years suggests that a booster dose is necessary to keep immunity against YF.

Analytical and clinical performances of five immunoassays for the detection of SARS-CoV-2 antibodies in comparison with neutralization activity

BACKGROUND

Reliable high-throughput serological assays for SARS-CoV-2 antibodies are urgently needed for the effective containment of the COVID-19 pandemic, as it is of crucial importance to understand the strength and duration of immunity after infection, and to make informed decisions concerning the activation or discontinuation of physical distancing restrictions.

METHODS

In 184 serum samples from 130 COVID-19 patients and 54 SARS-CoV-2 negative subjects, the analytical and clinical performances of four commercially available chemiluminescent assays (Abbott SARS-Cov-2 IgG, Roche Elecsys anti-SARS-CoV-2, Ortho SARS-CoV-2 total and IgG) and one enzyme-linked immunosorbent assay (Diesse ENZY-WELL SARS-CoV-2 IgG) were evaluated and compared with the neutralization activity achieved using the plaque reduction neutralization test (PRNT).

FINDINGS

Precision results ranged from 0.9% to 11.8% for all assays. Elecsys anti-SARS-CoV-2 demonstrated linearity of results at concentrations within the cut-off value. Overall, sensitivity ranged from 78.5 to 87.7%, and specificity, from 97.6 to 100%. On limiting the analysis to samples collected 12 days after onset of symptoms, the sensitivity of all assays increased, the highest value (95.2%) being obtained with VITRO Anti-SARS-CoV-2 Total and Architect SARS-CoV-2 IgG. The strongest PRNT50 correlation with antibody levels was obtained with ENZY-Well SARS-CoV-2 IgG (R2adj = 0.569).

INTERPRETATION

The results confirmed that all immunoassays had an excellent specificity, whereas sensitivity varied across immunoassays, depending strongly on the time interval between symptoms onset and sample collection. Further studies should be conducted to achieve a stronger correlation between antibody measurement and PRNT50 in order to obtain useful information for providing a better management of COVID-19 patients, effective passive antibody therapy, and developing a vaccine against the SARS-CoV-2 virus.

FUNDING

None.

The Neutralizing Antibody Response Elicited by Tembusu Virus Is Affected Dramatically by a Single Mutation in the Stem Region of the Envelope Protein

Tembusu virus (TMUV) is a mosquito-borne flavivirus that most commonly affects adult breeder and layer ducks. However, a TMUV-caused neurological disease has also been found in ducklings below 7 weeks of age, highlighting the need to develop a safe vaccine for young ducklings. In this study, a plaque-purified PS TMUV strain was attenuated by serial passage in BHK-21 cells. Using 1-day-old Pekin ducklings as a model, the virus was confirmed to be attenuated sufficiently after 180 passages, whereas the neutralizing antibody response elicited by the 180th passage virus (PS180) was substantially impaired compared with PS. The findings suggest that sufficient attenuation results in loss of immunogenicity in the development of the live-attenuated TMUV vaccine. Comparative sequence analysis revealed that PS180 acquired one mutation (V41M) in prM and four mutations (T70A, Y176H, K313R, and F408L) in the envelope (E) protein. To identify the amino acid substitution(s) associated with loss of immunogenicity of PS180, we rescued parental viruses, rPS and rPS180, and produced mutant viruses, rPS180-M41V, rPS180-A70T, rPS180-H176Y, rPS180-R313K, rPS180-L408F, and rPS180-M5, which contained residue 41V in prM, residues 70T, 176Y, 313K, and 408F in E, and combination of the five residues, respectively, of PS in the backbone of the rPS180 genome. The neutralizing antibody response elicited by rPS180-L408F and rPS180-M5 was significantly higher than those by other mutant viruses and comparable to that by rPS. Furthermore, we produced mutant virus rPS-F408L, which contained residue 408L of PS180 in the backbone of the rPS genome. The F408L mutation conferred significantly decreased neutralizing antibody response to rPS-F408L, which was comparable to that elicited by rPS180. Based on homologous modeling, residue 408 was predicted to be located within the first helical domain of the stem region of the E protein (EH1). Together, these data demonstrate that a single mutation within the EH1 domain exerts a dramatical impact on the TMUV neutralizing antibody response. The present work may enhance our understanding of molecular basis of the TMUV neutralizing antibody response, and provides an important step for the development of a safe and efficient live-attenuated TMUV vaccine.

A micro-PRNT for the detection of Ross River virus antibodies in mosquito blood meals: A useful tool for inferring transmission pathways

Introduction

Many arboviruses of public health significance are maintained in zoonotic cycles with complex transmission pathways. The presence of serum antibody against arboviruses in vertebrates provides evidence of their historical exposure but reveals nothing about the vector-reservoir relationship. Moreover, collecting blood or tissue samples from vertebrate hosts is ethically and logistically challenging. We developed a novel approach for screening the immune status of vertebrates against Ross River virus that allows us to implicate the vectors that form the transmission pathways for this commonly notified Australian arboviral disease.

Methods

A micro-plaque reduction neutralisation test (micro-PRNT) was developed and validated on koala (Phascolarctos cinereus) sera against a standard PRNT. The ability of the micro-PRNT to detect RRV antibodies in mosquito blood meals was then tested using two mosquito models. Laboratory-reared Aedes aegypti were fed, via a membrane, on sheep blood supplemented with RRV seropositive and seronegative human sera. Aedes notoscriptus were fed on RRV seropositive and seronegative human volunteers. Blood-fed mosquitoes were harvested at various time points after feeding and their blood meals analysed for the presence of RRV neutralising antibodies using the micro-PRNT.

Results

There was significant agreement of the plaque neutralisation resulting from the micro-PRNT and standard PRNT techniques (R² = 0.65; P<0.0001) when applied to RRV antibody detection in koala sera. Sensitivity and specificity of the micro-PRNT assay were 88.2% and 96%, respectively, in comparison with the standard PRNT. Blood meals from mosquitoes fed on sheep blood supplemented with RRV antibodies, and on blood from RRV seropositive humans neutralised the virus by ≥50% until 48 hr post feeding. The vertebrate origin of the blood meal was also ascertained for the same samples, in parallel, using established molecular techniques.

Conclusions

The small volumes of blood present in mosquito abdomens can be used to identify RRV antibodies and therefore host exposure to arbovirus infection. In tandem with the accurate identification of the mosquito, and diagnostics for the host origin of the blood meal, this technique has tremendous potential for exploring RRV transmission pathways. It can be adapted for similar studies on other mosquito borne zoonoses.

Planned Yellow Fever Primary Vaccination Is Safe and Immunogenic in Patients With Autoimmune Diseases: A Prospective Non-interventional Study

Yellow Fever (YF) vaccination is suggested to induce a large number of adverse events (AE) and suboptimal responses in patients with autoimmune diseases (AID); however, there have been no studies on 17DD-YF primary vaccination performance in patients with AID. This prospective non-interventional study conducted between March and July, 2017 assessed the safety and immunogenicity of planned 17DD-YF primary vaccination in patients with AID. Adult patients with AID (both sexes) were enrolled, along with healthy controls, at a single hospital (Vitória, Brazil). Included patients were referred for planned vaccination by a rheumatologist; in remission, or with low disease activity; and had low level immunosuppression or the attending physician advised interruption of immunosuppression for safety reasons. The occurrence of AE, neutralizing antibody kinetics, seropositivity rates, and 17DD-YF viremia were evaluated at various time points (day 0 (D0), D3, D4, D5, D6, D14, and D28). Individuals evaluated (n = 278), including patients with rheumatoid arthritis (RA; 79), spondyloarthritis (SpA; 59), systemic sclerosis (8), systemic lupus erythematosus (SLE; 27), primary Sjögren's syndrome (SS; 54), and healthy controls (HC; 51). Only mild AE were reported. The frequency of local and systemic AE in patients with AID and HC did not differ significantly (8 vs. 10% and 21 vs. 32%; p = 1.00 and 0.18, respectively). Patients with AID presented late seroconversion profiles according to kinetic timelines of the plaque reduction neutralization test (PRNT). PRNT-determined virus titers (copies/mL) [181 (95% confidence interval (CI), 144–228) vs. 440 (95% CI, 291–665), p = 0.004] and seropositivity rate (78 vs. 96%, p = 0.01) were lower in patients with AID after 28 days, particularly those with SpA (73%) and SLE (73%), relative to HC. The YF viremia peak (RNAnemia) was 5–6 days after vaccination in all groups. In conclusion, consistent seroconversion rates were observed in patients with AID and our findings support that planned 17DD-YF primary vaccination is safe and immunogenic in patients with AID.

A high infectious simian adenovirus type 23 vector based vaccine efficiently protects common marmosets against Zika virus infection

Zika virus (ZIKV) has spread in many countries or territories causing severe neurologic complications with potential fatal outcomes. The small primate common marmosets are susceptible to ZIKV, mimicking key features of human infection. Here, a novel simian adenovirus type 23 vector-based vaccine expressing ZIKV pre-membrane-envelope proteins (Sad23L-prM-E) was produced in high infectious titer. Due to determination of immunogenicity in mice, a single-dose of 3×10⁸ PFU Sad23L-prM-E vaccine was intramuscularly inoculated to marmosets. This vaccine raised antibody titers of 10^4.07 E-specific and 10^3.13 neutralizing antibody (NAb), as well as robust specific IFN-γ secreting T-cell response (1,219 SFCs/10⁶ cells) to E peptides. The vaccinated marmosets, upon challenge with a high dose of ZIKV (10⁵ PFU) six weeks post prime immunization, reduced viremia by more than 100 folds, and the low level of detectable viral RNA (<10³ copies/ml) in blood, saliva, urine and feces was promptly eliminated when the secondary NAb (titer >10^3.66) and T-cell response (>726 SFCs/10⁶ PBMCs) were acquired 1–2 weeks post exposure to ZIKV, while non-vaccinated control marmosets developed long-term high titer of ZIKV (10^5.73 copies/ml) (P<0.05). No significant pathological lesions were observed in marmoset tissues. Sad23L-prM-E vaccine was detectable in spleen, liver and PBMCs at least 4 months post challenge. In conclusion, a prime immunization with Sad23L-prM-E vaccine was able to protect marmosets against ZIKV infection when exposed to a high dose of ZIKV. This Sad23L-prM-E vaccine is a promising vaccine candidate for prevention of ZIKV infection in humans.

Zika virus (ZIKV) is a member of the Flaviviridaefamily) and causes severe neurologic diseases. The development of safe and effective vaccine is urgent need. In this study, we constructed a novel simian adenovirus type 23 vector-based vaccine expressing ZIKV pre-membrane-envelope proteins (Sad23L-prM-E). By vaccinating the common marmosets with prime immunization of vaccine, and upon challenge with a high dose of ZIKV to the vaccinated marmosets, the immune response and protective efficacy of vaccine were extensively evaluated. The data suggested that Sad23L-prM-E vaccine could protect marmosets against a high dose of ZIKV challenge, which provided a promising vaccine for preventing ZIKV infection in humans.

Detection of Neutralizing Antibodies to Tembusu Virus: Implications for Infection and Immunity

Neutralizing antibodies are the key mediators of protective immune response to flaviviruses after both infection and vaccination. Plaque reduction neutralization test (PRNT) is considered the “gold standard” for measurement of the immunity. To date, little is known regarding neutralizing antibody response to Tembusu virus (TMUV), a novel flavivirus emerging in ducks in 2010. Here, we developed a PRNT for detection of TMUV neutralizing antibodies. Following optimization and validation, the PRNT was applied to test serum samples from different flocks of ducks. Using sera prepared in experimental conditions, the levels of 50% end point titer (neutralizing dose, ND₅₀) generated from positive sera (5,012–79,433) were significantly higher than those from mock-infected sera (10 to 126), indicating that the test can be used in the detection of TMUV-specific neutralizing antibodies. Dose-dependent efficacy test of a cell-derived 180th passage of a plaque-purified virus of the PS TMUV isolate (PS180) in combined with immunization-challenge experiments revealed that ND₅₀ titer of ~1,258 is the minimum capable of providing adequate protection against challenge with virulent TMUV. In the investigation of serum samples collected from three flocks infected by TMUV and four flocks vaccinated with a licensed attenuated vaccine (the 120th passage virus), ND₅₀ titers peaked at 1 week after both disease onset (7,943–125,893) and vaccination (3,612–79,432), and high levels of ND₅₀ titer were detected in sera collected at 15 weeks after disease onset (5,012–63,095) and 17 weeks after vaccination (3,981–25,119). Together these findings demonstrated that spontaneous and experimental infections by TMUV and vaccination with the licensed TMUV attenuated vaccine elicit high, long-lasting neutralizing antibodies. The highest ND₅₀ titer of neutralizing antibodies elicited by PS180 was determined to be 3,162, suggesting that attenuation of TMUV by more passages has a dramatic impact on the neutralizing antibody response of the virus.

Multiplex PCR-based titration (MPBT) assay for determination of infectious titers of the three Sabin strains of live poliovirus vaccine

BACKGROUND

Conventional assays to titrate polioviruses usually test serial dilutions inoculated into replicate cell cultures to determine a 50% cytopathic endpoint, a process that is both time-consuming and laborious. Such a method is still used to measure potency of live Oral Poliovirus Vaccine during vaccine development and production and in some clinical trials. However, the conventional method is not suited to identify and titrate virus in the large numbers of fecal samples generated during clinical trials. Determining titers of each of the three Sabin strains co-existing in Oral Poliovirus Vaccine presents an additional challenge.

RESULTS

A new assay using quantitative multiplex polymerase chain reaction as an endpoint instead of cytopathic effect was developed to overcome these limitations. In the multiplex polymerase chain reaction-based titration assay, cell cultures were infected with serial dilutions of test samples, lysed after two-day incubation, and subjected to a quantitative multiplex one-step reverse-transcriptase polymerase chain reaction. All three serotypes of poliovirus were identified in single samples and titers calculated. The multiplex polymerase chain reaction-based titration assay was reproducible, robust and sensitive. Its lower limits of titration for three Sabin strains were 1-5 cell culture 50% infectious doses per ml. We prepared different combinations of three Sabin strains and compared titers obtained with conventional and multiplex polymerase chain reaction-based titration assays. Results of the two assays correlated well and showed similar results and sensitivity. Multiplex polymerase chain reaction-based titration assay was completed in two to 3 days instead of 10 days for the conventional assay.

CONCLUSIONS

The multiplex polymerase chain reaction-based titration (MPBT) is the first quantitative assay that identifies and titrates each of several different infectious viruses simultaneously in a mixture. It is suitable to identify and titrate polioviruses rapidly during the vaccine manufacturing process as a quality control test, in large clinical trials of vaccines, and for environmental surveillance of polioviruses. The MPBT assay can be automated for high-throughput implementation and applied for other viruses including those with no cytopathic effect.

Duration of post-vaccination humoral immunity against yellow fever in children

INTRODUCTION

Vaccination is the most important measure for prevention and control of yellow fever. It is recommended by the World Health Organization (WHO) for residents of endemic areas and travelers to risk areas. In 2013, the WHO discontinued the recommendation of booster doses every 10 years, indicating a single dose as sufficient for lifelong protection.

OBJECTIVE

Considering the lower immune response to YF vaccine in children compared to adults, this study was set out to assess the duration of immunity to YF in children vaccinated in the first two years of life.

METHODS

This cross-sectional study involved children aged 9 months to 12 years with accessible vaccination records recruited in primary care units from a metropolitan area in Southeast Brazil. The serologic status (negative, indeterminate and positive), and geometric mean titers (GMT, inverse dilution) of neutralizing antibodies against YF obtained by Plaque Reduction Neutralization Test was assessed across categories of time after YF vaccination. The strength of association of seropositivity with time was assessed by the odds ratio (OR) taking recent vaccination (1-6 months) as reference.

RESULTS

A total of 824 children recruited from August 2010 to July 2011were tested. The proportion of seropositivity (95% C.I.) and GMT (95% C.I.) dropped markedly across time periods: from 86.7% (80.5-91.4%), GMT 47.9 (38.3-59.9) in newly vaccinated to 59.0% (49.7-67.8%), GMT 14.8 (11.6-19.1) and 42.2% (33.8-51.0), GMT 8.6 (7.1-12.1), respectively in the subgroups vaccinated 31-72 months and 73-100 months before.

CONCLUSIONS

Analogous to previous findings in adults, these data support the need for revaccination of children living in areas with yellow fever virus circulation in humans or in other primates. The data also supported the change of a booster dose to 4 years of age for those primarily vaccinated for yellow fever in the first two years of life.

Short-Lived Immunity After 17DD Yellow Fever Single Dose Indicates That Booster Vaccination May Be Required to Guarantee Protective Immunity in Children

The Yellow Fever (YF) vaccination is recommended for people living in endemic areas and represents the most effective strategy to reduce the risk of infection. Previous studies have warned that booster regimens should be considered to guarantee the long-term persistence of 17DD-YF-specific memory components in adults living in areas with YF-virus circulation. Considering the lower seroconversion rates observed in children (9-12 months of age) as compared to adults, this study was designed in order to access the duration of immunity in single-dose vaccinated children in a 10-years cross-sectional time-span. The levels of neutralizing antibodies (PRNT) and the phenotypic/functional memory status of T and B-cells were measured at a baseline, 30-45 days, 1, 2, 4, 7, and 10 years following primary vaccination. The results revealed that a single dose induced 85% of seropositivity at 30-45 days and a progressive time-dependent decrease was observed as early as 2 years and declines toward critical values (below 60%) at time-spans of ≥4-years. Moreover, short-lived YF-specific cellular immunity, mediated by memory T and B-cells was also observed after 4-years. Predicted probability and resultant memory analysis emphasize that correlates of protection (PRNT; effector memory CD8+ T-cells; non-classical memory B-cells) wane to critical values within ≥4-years after primary vaccination. Together, these results clearly demonstrate the decline of 17DD-YF-specific memory response along time in children primarily vaccinated at 9-12 months of age and support the need of booster regimen to guarantee the long-term persistence of memory components for children living in areas with high risk of YF transmission.

17DD Yellow Fever Revaccination and Heightened Long-Term Immunity in Populations of Disease-Endemic Areas, Brazil

We evaluated the duration of neutralizing antibodies and the status of 17DD vaccine–specific T- and B-cell memory following primary and revaccination regimens for yellow fever (YF) in Brazil. We observed progressive decline of plaque-reduction neutralization test (PRNT) seropositivity and of the levels of effector memory CD4+ and CD8+ T cells, as well as interferon-γ+CD8+ T cells, 10 years after primary vaccination. Revaccination restored PRNT seropositivity as well as the levels of effector memory CD4+, CD8+, and interferon-γ+CD8+ T cells. Moreover, secondary or multiple vaccinations guarantee long-term persistence of PRNT positivity and cell-mediated memory 10 years after booster vaccination. These findings support the relevance of booster doses to heighten the 17DD-YF–specific immune response to guarantee the long-term persistence of memory components. Secondary or multiple vaccinations improved the correlates of protection triggered by 17DD-YF primary vaccination, indicating that booster regimens are needed to achieve efficient immunity in areas with high risk for virus transmission.

Brazilian recommendations on the safety and effectiveness of the yellow fever vaccination in patients with chronic immune-mediated inflammatory diseases

BACKGROUND

In Brazil, we are facing an alarming epidemic scenario of Yellow fever (YF), which is reaching the most populous areas of the country in unvaccinated people. Vaccination is the only effective tool to prevent YF. In special situations, such as patients with chronic immune-mediated inflammatory diseases (CIMID), undergoing immunosuppressive therapy, as a higher risk of severe adverse events may occur, assessment of the risk-benefit ratio of the yellow fever vaccine (YFV) should be performed on an individual level. Faced with the scarcity of specific orientation on YFV for this special group of patients, the Brazilian Rheumatology Society (BRS) endorsed a project aiming the development of individualized YFV recommendations for patients with CIMID, guided by questions addressed by both medical professionals and patients, followed an internationally validated methodology (GIN-McMaster Guideline Development). Firstly, a systematic review was carried out and an expert panel formed to take part of the decision process, comprising BRS clinical practitioners, as well as individuals from the Brazilian Dermatology Society (BDS), Brazilian Inflammatory Bowel Diseases Study Group (GEDIIB), and specialists on infectious diseases and vaccination (from Tropical Medicine, Infectious Diseases and Immunizations National Societies); in addition, two representatives of patient groups were included as members of the panel. When the quality of the evidence was low or there was a lack of evidence to determine the recommendations, the decisions were based on the expert opinion panel and a Delphi approach was performed. A recommendation was accepted upon achieving ≥80% agreement among the panel, including the patient representatives. As a result, eight recommendations were developed regarding the safety of YFV in patients with CIMID, considering the immunosuppression degree conferred by the treatment used. It was not possible to establish recommendations on the effectiveness of YFV in these patients as there is no consistent evidence to support these recommendations.

CONCLUSION

This paper approaches a real need, assessed by clinicians and patient care groups, to address specific questions on the management of YFV in patients with CIMID living or traveling to YF endemic areas, involving specialists from many areas together with patients, and might have global applicability, contributing to and supporting vaccination practices. We recommended a shared decision-making approach on taking or not the YFV.

Impact of synthetic and biological immunomodulatory therapy on the duration of 17DD yellow fever vaccine-induced immunity in rheumatoid arthritis

Background

The 17DD-yellow fever (YF) vaccine induces a long-lasting protective immunity, resulting from humoral and cellular immunological memory. The treatment of rheumatoid arthritis (RA) patients with disease-modifying anti-rheumatic drugs (DMARD) may affect pre-existing 17DD-vaccine protective immunity and increase the risk of acquiring YF infection. Our goal was to determine whether DMARD would affect the duration of YF-specific protective immunity in RA patients.

Methods

A total of 122 RA patients, previously immunized with the 17DD-YF vaccine (1–5, 5–9, and ≥ 10 years) and currently under DMARD therapy, were enrolled in the present investigation. Immunomodulatory therapy encompasses the use of conventional synthetic DMARD alone (csDMARD) or combines with biological DMARD (cs+bDMARD). A total of 226 healthy subjects were recruited as a control group (CONT). Neutralizing antibody responses were measured by a plaque-reduction neutralization test (PRNT), and cellular immunity was evaluated by an in vitro 17DD-YF-specific peripheral blood lymphoproliferative assay.

Results

The data demonstrated that csDMARD therapy did not affect the duration of protective immunity induced by the 17DD-YF vaccine compared to that of CONT, as both presented a significant time-dependent decline at 10 years after vaccination. Conversely, cs+bDMARD therapy induced a premature depletion in the main determinants of the vaccine protective response, with diminished PRNT seropositivity levels between 5 and 9 years and impaired effector memory in CD8⁺ T cells as early as 1–5 years after 17DD-YF vaccination.

Conclusions

These findings could support changing the vaccination schedule of this population, with the possibility of a planned booster dose upon the suspension of bDMARD in cases where this is allowed, even before 10 years following 17DD-YF vaccination. The benefit of a planned booster dose should be evaluated in further studies.

Trial registration

RBR-946bv5. Date of registration: March 05, 2018. Retrospectively registered

Mosquito-Borne Diseases

Mosquito-borne diseases have become more common as previously geographically isolated diseases have spread globally. Chikungunya, dengue, Japanese encephalitis, malaria, West Nile, yellow fever, and Zika are a few of the common and emerging viral diseases spread by mosquitoes. A thorough patient history, physical, and knowledge of diagnostic testing based on symptom duration is important to make a quick and accurate diagnosis. Because the treatment for many of these diseases is supportive, the emphasis is on reducing risk and spread of infection.

What Does the Future Hold for Yellow Fever Virus? (II)

As revealed by the recent resurgence of yellow fever virus (YFV) activity in the tropical regions of Africa and South America, YFV control measures need urgent rethinking. Over the last decade, most reported outbreaks occurred in, or eventually reached, areas with low vaccination coverage but that are suitable for virus transmission, with an unprecedented risk of expansion to densely populated territories in Africa, South America and Asia. As reflected in the World Health Organization's initiative launched in 2017, it is high time to strengthen epidemiological surveillance to monitor accurately viral dissemination, and redefine vaccination recommendation areas. Vector-control and immunisation measures need to be adapted and vaccine manufacturing must be reconciled with an increasing demand. We will have to face more yellow fever (YF) cases in the upcoming years. Hence, improving disease management through the development of efficient treatments will prove most beneficial. Undoubtedly, these developments will require in-depth descriptions of YFV biology at molecular, physiological and ecological levels. This second section of a two-part review describes the current state of knowledge and gaps regarding the molecular biology of YFV, along with an overview of the tools that can be used to manage the disease at the individual, local and global levels.

Multi-parameter approach to evaluate the timing of memory status after 17DD-YF primary vaccination

In this investigation, machine-enhanced techniques were applied to bring about scientific insights to identify a minimum set of phenotypic/functional memory-related biomarkers for post-vaccination follow-up upon yellow fever (YF) vaccination. For this purpose, memory status of circulating T-cells (Naïve/early-effector/Central-Memory/Effector-Memory) and B-cells (Naïve/non-Classical-Memory/Classical-Memory) along with the cytokine profile (IFN/TNF/IL-5/IL-10) were monitored before-NV(day0) and at distinct time-points after 17DD-YF primary vaccination—PV(day30-45); PV(year1-9) and PV(year10-11). A set of biomarkers (eEfCD4; EMCD4; CMCD19; EMCD8; IFNCD4; IL-5CD8; TNFCD4; IFNCD8; TNFCD8; IL-5CD19; IL-5CD4) were observed in PV(day30-45), but not in NV(day0), with most of them still observed in PV(year1-9). Deficiencies of phenotypic/functional biomarkers were observed in NV(day0), while total lack of memory-related attributes was observed in PV(year10-11), regardless of the age at primary vaccination. Venn-diagram analysis pre-selected 10 attributes (eEfCD4, EMCD4, CMCD19, EMCD8, IFNCD4, IL-5CD8, TNFCD4, IFNCD8, TNFCD8 and IL-5CD4), of which the overall mean presented moderate accuracy to discriminate PV(day30-45)&PV(year1-9) from NV(day0)&PV(year10-11). Multi-parameter approaches and decision-tree algorithms defined the EMCD8 and IL-5CD4 attributes as the top-two predictors with moderated performance. Together with the PRNT titers, the top-two biomarkers led to a resultant memory status observed in 80% and 51% of volunteers in PV(day30-45) and PV(year1-9), contrasting with 0% and 29% found in NV(day0) and PV(year10-11), respectively. The deficiency of memory-related attributes observed at PV(year10-11) underscores the conspicuous time-dependent decrease of resultant memory following17DD-YF primary vaccination that could be useful to monitor potential correlates of protection in areas under risk of YF transmission.

In this study, a set of immunological biomarkers was studied in order to understand protection upon vaccination with yellow fever (17DD-YF) vaccine. For this purpose, the immunological memory statuses of circulating T- and B-cells along with the plasmatic molecules (cytokine profile) were monitored before and at distinct time-points after primary vaccination. A set of biomarkers were measured in the peripheral blood of primary 17-DD vaccinees after 30–45 days of vaccination, which were relatively sustained in vaccinees after 1–9 years of primary vaccination. Deficiencies and a total lack of memory-related immunological responses to yellow fever virus were observed after 10 to 11 years post-vaccination, regardless of the age at primary vaccination. Multi-parameter approaches defined two biomarkers (EMCD8 and IL-5CD4) as the top-two predictors of protection. The deficiency of attributes observed after 10–11 years post-vaccination reveals a time-dependent decrease of immunological memory responses related to the 17DD-YF vaccination. Therefore, these results highly suggest the need for close attention to vaccinees in YF endemic areas with more than 10 years of vaccination. At last, the biomarkers proposed in this study could be useful to monitor protection in YF-vaccinees living in or travelling to areas under risk of YF transmission.

Plant-Produced Subunit Vaccine Candidates against Yellow Fever Induce Virus Neutralizing Antibodies and Confer Protection against Viral Challenge in Animal Models

Yellow fever (YF) is a viral disease transmitted by mosquitoes and endemic mostly in South America and Africa with 20-50% fatality. All current licensed YF vaccines, including YF-Vax^® (Sanofi-Pasteur, Lyon, France) and 17DD-YFV (Bio-Manguinhos, Rio de Janeiro, Brazil), are based on live attenuated virus produced in hens' eggs and have been widely used. The YF vaccines are considered safe and highly effective. However, a recent increase in demand for YF vaccines and reports of rare cases of YF vaccine-associated fatal adverse events have provoked interest in developing a safer YF vaccine that can be easily scaled up to meet this increased global demand. To this point, we have engineered the YF virus envelope protein (YFE) and transiently expressed it in Nicotiana benthamiana as a stand-alone protein (YFE) or as fusion to the bacterial enzyme lichenase (YFE-LicKM). Immunogenicity and challenge studies in mice demonstrated that both YFE and YFE-LicKM elicited virus neutralizing (VN) antibodies and protected over 70% of mice from lethal challenge infection. Furthermore, these two YFE-based vaccine candidates induced VN antibody responses with high serum avidity in nonhuman primates and these VN antibody responses were further enhanced after challenge infection with the 17DD strain of YF virus. These results demonstrate partial protective efficacy in mice of YFE-based subunit vaccines expressed in N. benthamiana. However, their efficacy is inferior to that of the live attenuated 17DD vaccine, indicating that formulation development, such as incorporating a more suitable adjuvant, may be required for product development.

Screening test for neutralizing antibodies against yellow fever virus, based on a flavivirus pseudotype

Given the possibility of yellow fever virus reintroduction in epidemiologically receptive geographic areas, the risk of vaccine supply disruption is a serious issue. New strategies to reduce the doses of injected vaccines should be evaluated very carefully in terms of immunogenicity. The plaque reduction test for the determination of neutralizing antibodies (PRNT) is particularly time-consuming and requires the use of a confinement laboratory. We have developed a new test based on the use of a non-infectious pseudovirus (WN/YF17D). The presence of a reporter gene allows sensitive determination of neutralizing antibodies by flow cytometry. This WN/YF17D test was as sensitive as PRNT for the follow-up of yellow fever vaccinees. Both tests lacked specificity with sera from patients hospitalized for acute Dengue virus infection. Conversely, both assays were strictly negative in adults never exposed to flavivirus infection or vaccination, and in patients sampled some time after acute Dengue infection. This WN/YF17D test will be particularly useful for large epidemiological studies and for screening for neutralizing antibodies against yellow fever virus.

Heparin removal by ecteola-cellulose pre-treatment enables the use of plasma samples for accurate measurement of anti-Yellow fever virus neutralizing antibodies

Technological innovations in vaccinology have recently contributed to bring about novel insights for the vaccine-induced immune response. While the current protocols that use peripheral blood samples may provide abundant data, a range of distinct components of whole blood samples are required and the different anticoagulant systems employed may impair some properties of the biological sample and interfere with functional assays. Although the interference of heparin in functional assays for viral neutralizing antibodies such as the functional plaque-reduction neutralization test (PRNT), considered the gold-standard method to assess and monitor the protective immunity induced by the Yellow fever virus (YFV) vaccine, has been well characterized, the development of pre-analytical treatments is still required for the establishment of optimized protocols. The present study intended to optimize and evaluate the performance of pre-analytical treatment of heparin-collected blood samples with ecteola-cellulose (ECT) to provide accurate measurement of anti-YFV neutralizing antibodies, by PRNT. The study was designed in three steps, including: I. Problem statement; II. Pre-analytical steps; III. Analytical steps. Data confirmed the interference of heparin on PRNT reactivity in a dose-responsive fashion. Distinct sets of conditions for ECT pre-treatment were tested to optimize the heparin removal. The optimized protocol was pre-validated to determine the effectiveness of heparin plasma:ECT treatment to restore the PRNT titers as compared to serum samples. The validation and comparative performance was carried out by using a large range of serum vs heparin plasma:ECT 1:2 paired samples obtained from unvaccinated and 17DD-YFV primary vaccinated subjects. Altogether, the findings support the use of heparin plasma:ECT samples for accurate measurement of anti-YFV neutralizing antibodies.

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

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.

Booster dose after 10 years is recommended following 17DD-YF primary vaccination

A single vaccination of Yellow Fever vaccines is believed to confer life-long protection. In this study, results of vaccinees who received a single dose of 17DD-YF immunization followed over 10 y challenge this premise. YF-neutralizing antibodies, subsets of memory T and B cells as well as cytokine-producing lymphocytes were evaluated in groups of adults before (NVday0) and after (PVday30-45, PVyear1-4, PVyear5-9, PVyear10-11, PVyear12-13) 17DD-YF primary vaccination. YF-neutralizing antibodies decrease significantly from PVyear1-4 to PVyear12-13 as compared to PVday30-45, and the seropositivity rates (PRNT≥2.9Log₁₀mIU/mL) become critical (lower than 90%) beyond PVyear5-9. YF-specific memory phenotypes (effector T-cells and classical B-cells) significantly increase at PVday30-45 as compared to naïve baseline. Moreover, these phenotypes tend to decrease at PVyear10-11 as compared to PVday30-45. Decreasing levels of TNF-α⁺ and IFN-γ⁺ produced by CD4⁺ and CD8⁺ T-cells along with increasing levels of IL-10⁺CD4⁺T-cells were characteristic of anti-YF response over time. Systems biology profiling represented by hierarchic networks revealed that while the naïve baseline is characterized by independent micro-nets, primary vaccinees displayed an imbricate network with essential role of central and effector CD8⁺ memory T-cell responses. Any putative limitations of this cross-sectional study will certainly be answered by the ongoing longitudinal population-based investigation. Overall, our data support the current Brazilian national immunization policy guidelines that recommend one booster dose 10 y after primary 17DD-YF vaccination.

CD4/CD8 Ratio and KT Ratio Predict Yellow Fever Vaccine Immunogenicity in HIV-Infected Patients

Background

HIV-infected individuals have deficient responses to Yellow Fever vaccine (YFV) and may be at higher risk for adverse events (AE). Chronic immune activation–characterized by low CD4/CD8 ratio or high indoleamine 2,3-dioxygenase-1 (IDO) activity—may influence vaccine response in this population.

Methods

We prospectively assessed AE, viremia by the YFV virus and YF-specific neutralizing antibodies (NAb) in HIV-infected (CD4>350) and -uninfected adults through 1 year after vaccination. The effect of HIV status on initial antibody response to YFV was measured during the first 3 months following vaccination, while the effect on persistence of antibody response was measured one year following vaccination. We explored CD4/CD8 ratio, IDO activity (plasma kynurenine/tryptophan [KT] ratio) and viremia by Human Pegivirus as potential predictors of NAb response to YFV among HIV-infected participants with linear mixed models.

Results

12 HIV-infected and 45-uninfected participants were included in the final analysis. HIV was not significantly associated with AE, YFV viremia or NAb titers through the first 3 months following vaccination. However, HIV–infected participants had 0.32 times the NAb titers observed for HIV-uninfected participants at 1 year following YFV (95% CI 0.13 to 0.83, p = 0.021), independent of sex, age and prior vaccination. In HIV-infected participants, each 10% increase in CD4/CD8 ratio predicted a mean 21% higher post-baseline YFV Nab titer (p = 0.024). Similarly, each 10% increase in KT ratio predicted a mean 21% lower post-baseline YFV Nab titer (p = 0.009). Viremia by Human Pegivirus was not significantly associated with NAb titers.

Conclusions

HIV infection appears to decrease the durability of NAb responses to YFV, an effect that may be predicted by lower CD4/CD8 ratio or higher KT ratio.

Yellow Fever (YF) vaccine is considered one of the most effective vaccines ever produced. However, previous studies suggest that HIV impairs YF vaccine response. In this study, we assessed if HIV infection impacts the risk of adverse events and could reduce antibody response to YF vaccine. We explored if laboratory markers of persistent inflammation, frequently present among HIV-infected patients, could predict antibody response to YF vaccine in this population. We found that HIV had no significant effect on adverse events or levels of antibodies through 3 months after vaccination, but this may be limited by the small sample size of 12 HIV-infected and 45-uninfected participants in the study. However, we were able to show that, compared to HIV-uninfected participants, HIV–infected patients had lower antibody titers 1 year following YF vaccine even after statistical adjustment for the potential effects of sex, age and prior vaccination. Persistent inflammation seems to reduce YF vaccine antibody response in HIV-infected participants. In conclusion, HIV-infected individuals have impaired antibody response to YFV due to a poorer persistence of antibodies, despite a seemingly normal initial response. HIV-infected patients at permanent or recurring risk of YF infection may benefit from a booster dose of YF vaccine.

CD4/CD8 Ratio Predicts Yellow Fever Vaccine-Induced Antibody Titers in Virologically Suppressed HIV-Infected Patients

BACKGROUND

Yellow fever vaccine (YFV) induces weaker immune responses in HIV-infected individuals. However, little is known about YFV responses among antiretroviral-treated patients and potential immunological predictors of YFV response in this population.

METHODS

We enrolled 34 antiretroviral therapy (ART)-treated HIV-infected and 58 HIV-uninfected adults who received a single YFV dose to evaluate antibody levels and predictors of immunity, focusing on CD4(+) T-cell count, CD4(+)/CD8(+) ratio, and Human Pegivirus (GBV-C) viremia. Participants with other immunosuppressive conditions were excluded.

RESULTS

Median time since YFV was nonsignificantly shorter in HIV-infected participants than in HIV-uninfected participants (42 and 69 months, respectively, P = 0.16). Mean neutralizing antibody (NAb) titers was lower in HIV-infected participants than HIV-uninfected participants (3.3 vs. 3.6 log10mIU/mL, P = 0.044), a difference that remained significant after adjustment for age, sex, and time since vaccination (P = 0.024). In HIV-infected participants, lower NAb titers were associated with longer time since YFV (rho: -0.38, P = 0.027) and lower CD4(+)/CD8(+) ratio (rho: 0.42, P = 0.014), but not CD4(+) T-cell count (P = 0.52). None of these factors were associated with NAb titers in HIV-uninfected participant. GBV-C viremia was not associated with difference in NAb titers overall or among HIV-infected participants.

CONCLUSIONS

ART-treated HIV-infected individuals seem to have impaired and/or less durable responses to YFV than HIV-uninfected individuals, which were associated with lower CD4(+)/CD8(+) ratio, but not with CD4(+) T-cell count. These results supports the notion that low CD4(+)/CD8(+) ratio, a marker linked to persistent immune activation, is a better indicator of functional immune disturbance than CD4(+) T-cell count in patients with successful ART.

Persistence of Yellow Fever vaccine-induced antibodies after cord blood stem cell transplant

We report the case of a cord blood haematopoietic stem cell transplant recipient who was vaccinated for Yellow Fever (YF) 7 days before initiating chemotherapy and had persistent YF antibodies more than 3 years after vaccination. Since the stem cell donor was never exposed to wild YF or to the YF vaccine, and our patient was not exposed to YF or revaccinated, this finding strongly suggests the persistence of recipient immunity. We briefly discuss potential consequences of incomplete elimination of recipient's leukocytes following existing haematopoietic cancer treatments.

An inactivated yellow fever 17DD vaccine cultivated in Vero cell cultures

Yellow fever is an acute infectious disease caused by prototype virus of the genus Flavivirus. It is endemic in Africa and South America where it represents a serious public health problem causing epidemics of hemorrhagic fever with mortality rates ranging from 20% to 50%. There is no available antiviral therapy and vaccination is the primary method of disease control. Although the attenuated vaccines for yellow fever show safety and efficacy it became necessary to develop a new yellow fever vaccine due to the occurrence of rare serious adverse events, which include visceral and neurotropic diseases. The new inactivated vaccine should be safer and effective as the existing attenuated one. In the present study, the immunogenicity of an inactivated 17DD vaccine in C57BL/6 mice was evaluated. The yellow fever virus was produced by cultivation of Vero cells in bioreactors, inactivated with β-propiolactone, and adsorbed to aluminum hydroxide (alum). Mice were inoculated with inactivated 17DD vaccine containing alum adjuvant and followed by intracerebral challenge with 17DD virus. The results showed that animals receiving 3 doses of the inactivated vaccine (2 μg/dose) with alum adjuvant had neutralizing antibody titers above the cut-off of PRNT50 (Plaque Reduction Neutralization Test). In addition, animals immunized with inactivated vaccine showed survival rate of 100% after the challenge as well as animals immunized with commercial attenuated 17DD vaccine.