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BACKGROUND: In 2021, four patients who had received solid organ transplants in the USA developed encephalitis beginning 2-6 weeks after transplantation from a common organ donor. We describe an investigation into the cause of encephalitis in these patients. METHODS: From Nov 7, 2021, to Feb 24, 2022, we conducted a public health investigation involving 15 agencies and medical centres in the USA. We tested various specimens (blood, cerebrospinal fluid, intraocular fluid, serum, and tissues) from the organ donor and recipients by serology, RT-PCR, immunohistochemistry, metagenomic next-generation sequencing, and host gene expression, and conducted a traceback of blood transfusions received by the organ donor. FINDINGS: We identified one read from yellow fever virus in cerebrospinal fluid from the recipient of a kidney using metagenomic next-generation sequencing. Recent infection with yellow fever virus was confirmed in all four organ recipients by identification of yellow fever virus RNA consistent with the 17D vaccine strain in brain tissue from one recipient and seroconversion after transplantation in three recipients. Two patients recovered and two patients had no neurological recovery and died. 3 days before organ procurement, the organ donor received a blood transfusion from a donor who had received a yellow fever vaccine 6 days before blood donation. INTERPRETATION: This investigation substantiates the use of metagenomic next-generation sequencing for the broad-based detection of rare or unexpected pathogens. Health-care workers providing vaccinations should inform patients of the need to defer blood donation for at least 2 weeks after receiving a yellow fever vaccine. Despite mitigation strategies and safety interventions, a low risk of transfusion-transmitted infections remains. FUNDING: US Centers for Disease Control and Prevention (CDC), the Biomedical Advanced Research and Development Authority, and the CDC Epidemiology and Laboratory Capacity Cooperative Agreement for Infectious Diseases.

AbstractIn the present study, an initial screening was conducted using 12 types of cell culture media, and four media with the best performance were selected for further study. The optimization of four media blend for YFV production was evaluated using an Augmented simplex centroid mixture design. Among all the different models that were investigated, the quadratic model was found to be the most appropriate model for exploring mixture design. It was found that M10 exhibited the greatest impact on YFV production, followed by M9, M4, and M1. The utilization of M1 and M4 media individually yielded higher compared to their blends with other media. The YFV titers were reduced when M1 media was combined with other media. The utilization of M9 and M10 media in combination resulted a higher viral yield compared to their respective concentrations. The optimal ratio for achieving a higher titer of YFV from primary CEFs was found to be approximately 38:62, with M9 and M10 being the most favorable media blend. The use of a media mixture led to a significant increase of virus titer up to 2.6 × 108 PFU/ml or 2 log titer yield, which is equivalent to 1.92 × 105 doses, without any changes to growth conditions or other process factors. This study concluded that the utilization of a mixture design could be efficiently employed to choose the optimal combination of media blends for enhanced viral production from cell culture. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

Abstract Introduction: In December 2016, an outbreak of sylvatic yellow fever (YF) occurred in the non-endemic areas of the south-eastern region of Brazil. The immune response to the yellow fever vaccine and its safety in individuals with chronic kidney disease (CKD) living in YF-endemic regions are not thoroughly understood. The objective of this study is to assess the incidence of adverse events and the serological response after primary vaccination with the 17DD-YF vaccine in CKD patients undergoing dialysis. Methods: This was a multicenter, retrospective cohort study involving 223 individuals with CKD who were on dialysis after primary vaccination against YF. Clinical and epidemiologic characteristics were collected and the vaccine adverse event (VAE) were assessed. Around 35 months after vaccination, the serological response was evaluated in 71 (32%) patients using neutralization tests. Results: No serious VAE occurred in any patient. Local reactions were reported in 13 individuals (5.8%), while 6 (2.7%) reported generalized systemic reactions and 205 (91.9%) did not display any VAE. No clinical or epidemiologic characteristic predicted the occurrence of VAE. Adequate serological response was found in 38% of participants and none of the clinical or epidemiological characteristics were associated with immunogenicity. Conclusion: The outcomes of our study suggest that the yellow YF vaccine is well-tolerated in CKD patients undergoing dialysis, but it does not induce adequate immune response. Future research should focus on evaluating both cellular and humoral immune responses following administration of various doses of the YF vaccine.

Objective: Evaluate biomarkers capable of safely guiding Yellow fever vaccine (YFV) vaccination among individuals suspicious of hen's egg allergy, and identify factors associated with a higher risk for adverse events after immunization (AEAI). Methods: Patients underwent skin prick test (SPT) for standardized allergens: whole egg, egg white, egg yolk; YFV (1:10 dilution; Biomanguinhos-Fiocruz), and intradermal test (IDT; YFV 0.02 mL, 1:100 dilution) and positive and negative controls. Serum levels of specific IgE (sIgE) for a whole egg, egg white, egg yolk, egg albumin, ovomucoid, lysozyme, and conalbumin (ImmunoCap®; ThermoFisher®) were obtained. Patients sensitized to YFV were submitted to YFV desensitization, and those negatives received YFV (0.5mL) and remained under surveillance for at least one hour. Results: 103 patients were enrolled, 95% under 12 years old. 71% (81/103) of patients had reactions: 80% immediate, 11% mixed, and 9% delayed. There was an association between positive skin test results with YFV and the severity of the reaction (OR:7.64; 95%CI:1.61-36.32; p = 0,011). Only the presence of sIgE to ovomucoid was associated with clinical symptoms (p = 0,025). Thirty patients underwent the YFV desensitization protocol. Conclusion: There is a relationship between the positivity of the egg's components and the severity of the clinical reaction. Furthermore, the relationship between the positivity of the tests with the YFV and egg's components may show a tendency to look at ovomucoid and conalbumin, but it is not a certainty. Therefore, further studies are needed to confirm these associations, and for now, the authors still recommend using the vaccine for testing when necessary. [ABSTRACT FROM AUTHOR]

This article discusses a study conducted in Barcelona, Spain, which aimed to investigate the potential protective effects of prior yellow fever vaccination against COVID-19. The study involved adult participants who visited a clinic for travel medicine recommendations and vaccinations. The findings of the study showed no significant association between prior yellow fever vaccination and the incidence or severity of COVID-19. The study also identified associations between certain comorbidities and non-infection, possibly due to stricter COVID-19 measures followed by individuals with these conditions. However, the study acknowledges limitations such as the small sample size and the use of self-reported online questionnaires. Overall, the study suggests that prior yellow fever vaccination does not provide protection against COVID-19. [Extracted from the article]

Between 2016 and 2018, Brazil faced a yellow fever (YF) outbreak, which led to an expansion of vaccination coverage. The coexistence of the YF outbreak and the HIV-1 epidemic in Brazil raised concerns regarding the immune response and vaccine effectiveness in individuals living with HIV (PLWH). The aim of this study was to investigate the immune response to YF vaccination in PLWH and HIV-uninfected individuals as controls. Transcript levels of immunomodulatory molecules, including IL-6, IL-10, IL-21, TGF-β, CD19, CD163, miR-21, miR-146, and miR-155, were measured using RT qPCR. TCD4+ cells were evaluated by cytometry, and neutralizing antibody (Nab) titers were detected by a micro plaque-reduction neutralization test. The findings of our study revealed several noteworthy observations. First, there was a notable reduction in the circulation of TCD4+ cells postvaccination. Among people living with HIV (PLWH), we observed an increase in the expression of IL-10 following vaccination, while IL-6 expression was diminished in PLWH with lower TCD4+ counts. Furthermore, we identified the downregulation of CD19 and TGF-β, along with the upregulation of IL-21 and CD163. Notably, we observed positive correlations between the levels of IL-10/IL-21, IL-10/CD163, and IL-6/CD19. Additionally, there was a positive correlation between miRNAs 146 and 155. It is important to emphasize that all participants exhibited robust neutralizing antibody responses after receiving 17DD YF vaccination. In this context, the gene expression data presented can be useful for biomarker studies of protective antibodies induced by YF vaccination. This study sheds light on immune mechanisms in individuals living with HIV and YF vaccination. • The yellow fever vaccine (YFV) induced a decrease in circulating CD4+ T cells. • Individuals living with HIV (PLWH) achieved levels of antibodies neutralizing against YF. • YFV induced different levels of IL-10 expression between PLWH and controls. • Correlations between cytokines showed crosstalk in the YF vaccine immune response. [ABSTRACT FROM AUTHOR]

Background YF-VAX® (Sanofi, Swiftwater, PA), a live, attenuated vaccine based on the yellow fever (YF) substrain 17D-204, is the only YF vaccine licensed in the USA. Manufacturing disruption of YF-VAX and anticipated depletion of the US supply by mid-2017 led to the importation of another YF vaccine, STAMARIL® (Sanofi, France), into the USA under an expanded access investigational new drug program (EAP) to fulfil the public health need for YF vaccination. As part of this program, Sanofi collected enhanced safety surveillance data following vaccination with STAMARIL. Here, we report the results of the enhanced safety surveillance. Methods STAMARIL vaccine was offered to those aged ≥9 months at high risk of YF. Vaccine recipients (or parents/guardians) were instructed to report suspected adverse reactions, any serious adverse events (SAEs) including adverse events of special interest [AESI] occurring after vaccination regardless of suspected relationship, and any inadvertent exposure in pregnancy or breastfeeding within 14 days of vaccination. The AESIs monitored were anaphylaxis, neurotropic disease (YEL-AND) and viscerotropic disease (YEL-AVD). Results Overall, 627 079 individuals received STAMARIL from May 2017 through June 2021; of these, 1308 (0.2%) reported at least one AE, of which 122 reported at least one SAE. There were seven cases of YEL-AND and three cases of YEL-AVD reported, for reporting rates of 1.1 and 0.5 per 100 000 vaccine recipients, respectively. One vaccine recipient developed an anaphylactic reaction (reporting rate: 0.16 per 100 000). No safety concerns were identified from inadvertent vaccine exposure during pregnancy (41 pregnant women) or potential neonatal exposure via breast milk (four exposed infants). Conclusions This study supports the utility of STAMARIL in the EAP as an alternative solution for the YF vaccine shortage in the USA. SAEs were very rare and consistent with the known safety profile of STAMARIL. [ABSTRACT FROM AUTHOR]

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.

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 3. 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.

We describe 5 cases of yellow fever vaccine–associated viscerotropic disease (YEL-AVD) in 2 familial clusters during the 2017–2018 yellow fever (YF) vaccination campaign in São Paulo state, Brazil. The first case was that of a 40-year-old white man who died of icterohemorrhagic syndrome, which was confirmed to be YEL-AVD by using real-time reverse transcription PCR to detect 17DD YF vaccine in the liver. Ten years previously, his brother died of a clinically similar disease without a confirmed diagnosis 9 days after YF vaccination. The second cluster included 3 of 9 siblings in whom hepatitis developed in the first week after receiving fractionated doses of YF vaccine. Two of them died of hemorrhagic diathesis and renal and respiratory failure, and 17DD-YF vaccine was detected in serum samples from all patients and in the liver in 1 case. Genetic factors might play a substantial role in the incidence of YEL-AVD.

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Background Yellow fever (YF) is an arbovirus with variable severity, including severe forms with high mortality. The vaccination is the most effective measure to protect against the disease. Non-serious and serious adverse events have been described in immunocompromised individuals, but previous studies have failed to demonstrate this association. This systematic review assessed the risk of adverse events after YF vaccination in immunocompromised individuals compared with its use in non-immunocompromised individuals. Methods A search was conducted in the MEDLINE, LILACS, EMBASE, SCOPUS, DARE, Toxiline, Web of Science and grey literature databases for publications until February 2021. Randomized and quasi-randomized clinical trials and observational studies that included immunocompromised participants (individuals with HIV infection, organ transplants, with cancer, who used immunosuppressive drugs for rheumatologic diseases and those on immunosuppressive therapy for other diseases) were selected. The methodological quality of observational or non-randomized studies was assessed by the ROBINS-I tool. Two meta-analyses were performed, proportion and risk factor analyses, to identify the summary measure of relative risk (RR) in the studies that had variables suitable for combination. Results Twenty-five studies were included, most with risk of bias classified as critical. Thirteen studies had enough data to carry out the proposed meta-analyses. Seven studies without a comparator group had their results aggregated in the proportion meta-analysis, identifying an 8.5% [95% confidence interval (CI) 0.07–21.8] risk of immunocompromised individuals presenting adverse events after vaccination. Six cohort studies were combined, with an RR of 1.00 (95% CI 0.78–1.29). Subgroup analysis was performed according to the aetiology of immunosuppression and was also unable to identify an increased risk of adverse events following vaccination. Conclusions It is not possible to affirm that immunocompromised individuals, regardless of aetiology, have a higher risk of adverse events after receiving the YF vaccine. [ABSTRACT FROM AUTHOR]

The duration of protection after a single dose of yellow fever vaccine is a matter of debate. To summarize the current knowledge, we performed a systematic literature review and meta-analysis. Studies on the duration of protection after 1 and ≥2 vaccine doses were reviewed. Data were stratified by time since vaccination. In our meta-analysis, we used random-effects models. We identified 36 studies from 20 countries, comprising more than 17 000 participants aged 6 months to 85 years. Among healthy adults and children, pooled seroprotection rates after single vaccination dose were close to 100% by 3 months and remained high in adults for 5 to 10 years. In children vaccinated before age 2 years, the seroprotection rate was 52% within 5 years after primary vaccination. For immunodeficient persons, data indicate relevant waning. The extent of waning of seroprotection after yellow fever vaccination depends on age and immune status at primary vaccination. [ABSTRACT FROM AUTHOR]

• The vYF-247 vaccine candidate strain was obtained from YF-VAX by clone purification. • Genetic stability and consistency of vYF-247 was demonstrated during manufacture. • vYF-247 had a consistent small plaque size profile (<1 mm) during manufacture. • vYF-247 had a more attenuated neurovirulence phenotype during production than YF-VAX. • The safety profile of vYF-247 is anticipated to be favorable in clinical practice. We assessed the genetic and phenotypic characteristics of a yellow fever vaccine candidate, which was cloned from a YF-VAX substrain selected for growth in Vero cells (vYF-247), during the manufacturing process from the master seed lot (MSL) and working seed lot (WSL) through to the drug substance (DS) stage. There were nine minor nucleotide variants observed from the MSL to the DS stage, of which five led to amino acid changes. The variant positions were, however, not known risks for any virulence modification. vYF-247 exhibits a homogenous plaque size profile (as expected for a cloned vaccine candidate) composed of small plaques (<1 mm) that remained consistent throughout the manufacturing process. In addition, there was no change in the viral replication rate. Of note, the DS sequences across the two manufacturing campaigns (2018 and 2019) were very similar suggesting a high batch-to-batch consistency. All MSL, WSL and DS batches exhibited similar neurovirulence profiles in mice and had a more attenuated neurovirulence phenotype than the YF-VAX (egg-based vaccine) comparator. Overall, the neurovirulence phenotype of vYF-247 does not change from MSL, WSL to DS. These data collectively support the safety and genetic stability of vYF-247 during the production process. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To report an unusual case of corneal graft rejection after yellow fever vaccine. Case report. We have described the case of a 48-year-old man who developed a corneal graft rejection in the left eye 3 weeks after a yellow fever vaccination. The ophthalmic examination of the left eye revealed conjunctival hyperemia, corneal graft edema with Descemet folds, and fine keratic precipitates. No abnormalities were found in the right eye. The episode of graft rejection fully recovered after a short course of systemic and topical steroid treatment. This is the first case report of corneal transplant rejection temporally associated with yellow fever vaccination. Although the yellow fever vaccine is a very safe and efficacious vaccine, the occurrence of vaccine-related rejection may be more frequent than reported. Both patients and ophthalmologists should be aware of possible vaccine-related complications which may be potentially sight-threatening. [ABSTRACT FROM AUTHOR]

Objectives: In 2017, the World Health Organisation (WHO) pre-qualified a single-dose typhoid conjugate vaccine (TCV) and identified TCV co-administration studies as a research priority. Accordingly, we tested co-administration of Typbar TCV® (Bharat Biotech International) with measles-rubella (MR) and yellow fever (YF) vaccines. Methods: We conducted a randomized, double-blind, and controlled, phase 2 trial in Ouagadougou, Burkina Faso. Healthy children aged 9–11 months were randomized 1:1 to receive TCV (Group 1) or control vaccine (inactivated polio vaccine (IPV), Group 2). Vaccines were administered intramuscularly with routine MR and YF vaccines. Safety was assessed by (1) local and systemic reactions on days 0, 3, and 7; (2) unsolicited adverse events within 28 days; and (3) serious adverse events (SAEs) within six months after immunization. Results: We enrolled, randomized, and vaccinated 100 eligible children (49 Group 1 and 51 Group 2). Safety outcomes occurred with similar frequency in both groups: local/solicited reactions (Group 1: 1/49, Group 2: 3/50), systemic/solicited reactions (Group 1: 4/49, Group 2: 9/50), unsolicited adverse events (Group 1: 26/49, Group 2: 33/51), and SAEs (Group 1: 2/49, Group 2: 3/51). TCV conferred robust immunogenicity without interference with MR or YF vaccines. Conclusion: TCV can be safely co-administered with MR and YF vaccines to children at the 9-month vaccination visit.

Summary: Background: The live-attenuated yellow fever vaccine YF17D holds great promise as alternative viral vector vaccine platform, showcased by our previously presented potent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine candidate YF-S0. Besides protection from SARS-CoV-2, YF-S0 also induced strong yellow fever virus (YFV)-specific immunity, suggestive for full dual activity. A vaccine concomitantly protecting from SARS-CoV-2 and YFV would be of great benefit for those living in YFV-endemic areas with limited access to current SARS-CoV-2 vaccines. However, for broader applicability, pre-existing vector immunity should not impact the potency of such YF17D-vectored vaccines. Methods: The immunogenicity and efficacy of YF-S0 against YFV and SARS-CoV-2 in the presence of strong pre-existing YFV immunity were evaluated in mouse and hamster challenge models. Findings: Here, we show that a single dose of YF-S0 is sufficient to induce strong humoral and cellular immunity against YFV as well as SARS-CoV-2 in mice and hamsters; resulting in full protection from vigorous YFV challenge in either model; in mice against lethal intracranial YF17D challenge, and in hamsters against viscerotropic infection and liver disease following challenge with highly pathogenic hamster-adapted YFV-Asibi strain. Importantly, strong pre-existing immunity against the YF17D vector did not interfere with subsequent YF-S0 vaccination in mice or hamsters; nor with protection conferred against SARS-CoV-2 strain B1.1.7 (Alpha variant) infection in hamsters. Interpretation: Our findings warrant the development of YF-S0 as dual SARS-CoV-2 and YFV vaccine. Contrary to other viral vaccine platforms, use of YF17D does not suffer from pre-existing vector immunity. Funding: Stated in the acknowledgments.

We conducted a systematic review and a meta-analysis to assess the risk of serious adverse events in the elderly after yellow fever vaccination compared to the non-elderly population. We searched multiple databases and grey literature, and we selected research without language and publication date restrictions. Studies were analyzed in a descriptive way and meta-analyzed and expressed in terms of prevalence ratio and risk ratio with a 95% confidence interval, depending on the degree of heterogeneity found. A total of 18 studies were included and 11 were meta-analyzed. The results obtained through the meta-analysis showed a risk of serious adverse events after yellow fever vaccination three times higher for the elderly when compared to the non-elderly population and five times higher for persons > 70 years. In relation to adverse event types, viscerotropic disease associated with the yellow fever vaccine had a risk that was six times higher when compared to the population < 60 years. The evidence found supports that the vaccine indication in individuals > 60 years of age should be based on a careful analysis of individual benefit-risk assessments. The results found suggest a higher risk of events for individuals > 70 years, especially for viscerotropic and neurotropic disease associated with YFV contraindicating the use of the YFV in this age group. [ABSTRACT FROM AUTHOR]

BackgroundHIV-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.MethodsWe 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.Results12 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.ConclusionsHIV 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.

ABSTRACT OBJECTIVE To analyze the number of yellow fever vaccine doses administered before and during the covid-19 pandemic in Brazil. METHODS This is an ecological, time series study based on data from the National Immunization Program. Differences between the median number of yellow fever vaccine doses administered in Brazil and in its regions before (from April/2019 to March/2020) and after (from April/2020 to March/2021) the implementation of social distancing measures in the country were assessed via the Mann-Whitney test. Prais-Winsten regression models were used for time series analyses. RESULTS We found a reduction in the median number of yellow fever vaccine doses administered in Brazil and in its regions: North (-34.71%), Midwest (-21.72%), South (-63.50%), and Southeast (-34.42%) (p < 0.05). Series showed stationary behavior in Brazil and in its five regions during the covid-19 pandemic (p > 0.05). Brazilian states also showed stationary trends, except for two states which recorded an increasing trend in the number of administered yellow fever vaccine doses, namely: Alagoas State (before: β = 64, p = 0.081; after: β = 897, p = 0.039), which became a yellow fever vaccine recommendation zone, and Roraima State (before: β = 68, p = 0.724; after: β = 150, p = 0.000), which intensified yellow fever vaccinations due to a yellow fever case confirmation in a Venezuelan State in 2020. CONCLUSION The reduced number of yellow fever vaccine doses administered during the covid-19 pandemic in Brazil may favor the reemergence of urban yellow fever cases in the country.

Abstract Background Yellow Fever (YF) immunization required a single dose vaccine with boosters every 10 years. After International Health Regulation (IHR) amendment annex 7 (July 2016), it was accepted that a single dose confers lifelong immunity. Since pre-travel advice is as important as vaccination when traveling, it is essential to clarify why travelers come to a travel health consultation, with the possibility of IHR amendment having a negative impact on travelers’ health. This study aims to describe travelers’ reasons to come to a pre-travel consultation in Lisbon and if they would return if they wouldn’t need the YF vaccine booster. Methods An observational cross-sectional study was conducted during 5 months in the waiting room of Instituto de Higiene e Medicina Tropical travel clinic in Lisbon, Portugal. Travelers were asked about sociodemographic characteristics, destination country, travel duration and reasons to travel in an anonymous self-administered questionnaire. Results A total of 1043 travelers agreed to participate in the study. Although 61.0% (627/1028) did not come to the clinic to get the YF vaccine, from those who did, 36.7% (133/362) would not come and 12.9% (47/362) didn’t knew if they would come if the vaccine would not be necessary. Conclusion The IHR amendment may have a negative impact on travel clinic attendance and on travelers´ health.

Yellow fever vaccine-associated neurotropic disease (YEL-AND) is a rare and serious complication following vaccination with the 17D live attenuated yellow fever vaccine. Cases of YEL-AND have presented as acute inflammatory demyelinating polyneuropathy, acute disseminated encephalomyelitis, and meningoencephalitis. To date, intracranial imaging of the progression and resolution of this disease has been minimally depicted in the literature. We present the case of a 67-year-old woman who developed YEL-AND following vaccination. Her diagnosis was complicated by imaging findings consistent with variant Creutzfeldt Jakob Disease. Her clinical history and the progression of her intracranial imaging is discussed in this case report. [ABSTRACT FROM AUTHOR]

• We assessed greater than 10 years of civilian YF vaccinee data in 3 US healthcare databases. • Most YF vaccinees were aged < 60 years (largest age group 18–29 years). • Few vaccinees (<1%) had medical conditions predisposing them to immunosuppression. • Incidence proportion of neurotropic disease ranged from 0 to 3.04 per 100,000 vaccinees. • There were no viscerotropic cases identified across the three databases assessed. Yellow fever (YF) vaccines are highly effective and have a well-established safety profile despite the risk of rare serious adverse events (SAEs), vaccine-associated neurotropic (YEL-AND) and viscerotropic disease (YEL-AVD). This study aimed to describe US civilian YF vaccine usage, the population characteristics and pre-existing immunosuppressive medical conditions among those vaccinated, and to provide updated risk estimates of neurotropic and viscerotropic disease post-vaccination. A retrospective cohort study was conducted using de-identified patient information from Optum Electronic Healthcare Record (EHR) (2007–2019), Optum Clinformatics Data Mart (CDM) (2004–2019) and IBM MarketScan (2007–2019) databases. YF vaccine recipients were identified using relevant vaccination and procedural codes. Demographic characteristics and pre-existing medical conditions were described. Incidence proportions with 95% confidence intervals (CI) of neurotropic and viscerotropic diseases occurring ≤ 30 days post-vaccination, after exclusion of unlikely cases based on current clinical guidelines of YEL-AND and YEL-AVD, were calculated. A total of 92,205, 46,539 and 125,235 YF vaccine recipients were retrieved from Optum EHR, Optum CDM and IBM MarketScan databases, respectively. The majority of vaccine recipients were aged < 60 years (highest proportion aged 18–29 years) with a higher proportion of females overall. Few vaccine recipients (<1%) had conditions predisposing them to immunosuppression. Four non-fatal cases of neurotropic disease and zero cases of viscerotropic disease were identified. The incidence proportion of post-vaccination neurotropic disease was 1.41 (95% CI: 0.15–6.61) and 3.04 (95% CI: 0.86–8.11) per 100,000 vaccine recipients in Optum EHR and IBM MarketScan, respectively, with no events identified in Optum CDM. This study provides updated insights into current YF vaccine usage in US civilian recipients and supports the safety profile of YF vaccines in US practice. The low frequency of pre-existing immunosuppressive medical conditions among vaccine recipients suggests good adherence to vaccination guidelines by healthcare practitioners. The risk of developing neurotropic and viscerotropic disease post-vaccination remains rare. [ABSTRACT FROM AUTHOR]

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OBJECTIVE: To analyze the number of yellow fever vaccine doses administered before and during the covid-19 pandemic in Brazil. METHODS: This is an ecological, time series study based on data from the National Immunization Program. Differences between the median number of yellow fever vaccine doses administered in Brazil and in its regions before (from April/2019 to March/2020) and after (from April/2020 to March/2021) the implementation of social distancing measures in the country were assessed via the Mann-Whitney test. Prais-Winsten regression models were used for time series analyses. RESULTS: We found a reduction in the median number of yellow fever vaccine doses administered in Brazil and in its regions: North (-34.71%), Midwest (-21.72%), South (-63.50%), and Southeast (-34.42%) (p < 0.05). Series showed stationary behavior in Brazil and in its five regions during the covid-19 pandemic (p > 0.05). Brazilian states also showed stationary trends, except for two states which recorded an increasing trend in the number of administered yellow fever vaccine doses, namely: Alagoas State (before: ß = 64, p = 0.081; after: ß = 897, p = 0.039), which became a yellow fever vaccine recommendation zone, and Roraima State (before: ß = 68, p = 0.724; after: ß = 150, p = 0.000), which intensified yellow fever vaccinations due to a yellow fever case confirmation in a Venezuelan State in 2020. CONCLUSION: The reduced number of yellow fever vaccine doses administered during the covid-19 pandemic in Brazil may favor the reemergence of urban yellow fever cases in the country. [ABSTRACT FROM AUTHOR]

Yellow fever vaccine-associated neurotropic disease (YEL-AND) is a rare and serious complication following vaccination with the 17D live attenuated yellow fever vaccine. Cases of YEL-AND have presented as acute inflammatory demyelinating polyneuropathy, acute disseminated encephalomyelitis, and meningoencephalitis. To date, intracranial imaging of the progression and resolution of this disease has been minimally depicted in the literature. We present the case of a 67-year-old woman who developed YEL-AND following vaccination. Her diagnosis was complicated by imaging findings consistent with variant Creutzfeldt Jakob Disease. Her clinical history and the progression of her intracranial imaging is discussed in this case report.

Despite the existence of a highly efficient yellow fever vaccine, yellow fever reemergence throughout Africa and the Americas has put 900 million people in 47 countries at risk of contracting the disease. Although the vaccine has been key to controlling yellow fever epidemics, its live-attenuated nature comes with a range of contraindications that prompts advising against its administration to pregnant and lactating women, immunocompromised individuals, and those with hypersensitivity to chicken egg proteins. Additionally, large outbreaks have highlighted problems with insufficient vaccine supply, whereby manufacturers rely on slow traditional manufacturing processes that prevent them from ramping up production. These limitations have contributed to an inadequate control of yellow fever and have favored the pursuit of novel yellow fever vaccine candidates that aim to circumvent the licensed vaccine’s restrictions. Here, we review the live-attenuated vaccine’s limitations and explore the epitome of a yellow fever vaccine, whilst scrutinizing next-generation vaccine candidates.

Background: In 2013, the World Health Organization (WHO) revised their position on yellow fever vaccination, in which revaccination every 10 years was no longer required, and that a single-dose provided life-long protection. However, research data on the immunogenicity of YF vaccine in people aged 60 years and over are scarce. Indeed, immunosenescence may result in lower virus neutralizing antibody titers after primary vaccination and a more rapid waning immunity. Therefore, we tested the hypothesis that older travelers, vaccinated at 60 years or older are more likely to become seronegative in comparison to young adults 10 years after primary YF vaccination.Methods: This is a 10-year follow-up study of an earlier prospective controlled cohort study. In the original trial, the neutralizing antibody response was measured in older travelers (aged 60-81 years, N = 28) and young adults (aged 18-28 years, N = 30) up to 28 days after a primary yellow fever vaccination. Ten years later, we collected serum samples of 22/28 (78%) elderly (71-85 years) and 14/30 (47%) controls (29-40 years), and determined their neutralizing antibody titers by plaque reduction neutralization test (PRNT80). Seropositivity was defined as plaque formation reduction of 80% at a serum dilution of 10 or more (PRNT80 ≥ 10).Results: All participants (36/36) were still seropositive 10 years after primary vaccination. The geometric mean concentrations were not statistically different between the older and younger participants (6.7 IU/mL vs. 8.6 IU/mL, P = 0.5).Conclusions: All older travelers were seropositive, 10 years after a primary YF vaccination at the age of ≥60 years. These data suggest that in older travelers a single vaccination is sufficient to convey long-lasting immunity for at least 10 years, and is in support the position of the WHO on a single-dose yellow fever vaccination. [ABSTRACT FROM AUTHOR]

Abstract Background Yellow fever vaccine exists for over 80 years and is considered to be relatively safe. However, in rare cases it can produce serious neurotropic and viscerotropic complications. We report a case of a patient who presented both viscerotropic and neurological manifestations after yellow fever vaccination. Case presentation We describe the case of a 37 years old man who developed after the yellow fever vaccination a yellow fever vaccine-associated viscerotropic disease followed by acute uveitis. Prolonged detection of yellow fever RNA in blood and urine was consistent with yellow fever vaccine-associated adverse event. The final outcome was good, although with persistent fatigue over a few months. Conclusions Even if the yellow fever vaccine is relatively safe, physicians should be aware of its possible serious adverse effects.

Abstract Background Different human responses to the same vaccine were frequently observed. For example, independent studies identified overlapping but different transcriptomic gene expression profiles in Yellow Fever vaccine 17D (YF-17D) immunized human subjects. Different experimental and analysis conditions were likely contributed to the observed differences. To investigate this issue, we developed a Vaccine Investigation Ontology (VIO), and applied VIO to classify the different variables and relations among these variables systematically. We then evaluated whether the ontological VIO modeling and VIO-based statistical analysis would contribute to the enhanced vaccine investigation studies and a better understanding of vaccine response mechanisms. Results Our VIO modeling identified many variables related to data processing and analysis such as normalization method, cut-off criteria, software settings including software version. The datasets from two previous studies on human responses to YF-17D vaccine, reported by Gaucher et al. (2008) and Querec et al. (2009), were re-analyzed. We first applied the same LIMMA statistical method to re-analyze the Gaucher data set and identified a big difference in terms of significantly differentiated gene lists compared to the original study. The different results were likely due to the LIMMA version and software package differences. Our second study re-analyzed both Gaucher and Querec data sets but with the same data processing and analysis pipeline. Significant differences in differential gene lists were also identified. In both studies, we found that Gene Ontology (GO) enrichment results had more overlapping than the gene lists and enriched pathway lists. The visualization of the identified GO hierarchical structures among the enriched GO terms and their associated ancestor terms using GOfox allowed us to find more associations among enriched but often different GO terms, demonstrating the usage of GO hierarchical relations enhance data analysis. Conclusions The ontology-based analysis framework supports standardized representation, integration, and analysis of heterogeneous data of host responses to vaccines. Our study also showed that differences in specific variables might explain different results drawn from similar studies.

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., (© 2024. The Author(s).)

• This is the first study on the co-administration of typhoid conjugate vaccine (TCV) in West Africa. • Co-administration of TCV with routine vaccines in a typhoid-endemic country was successful. • TCV was safely co-administered at nine months with yellow fever and measles-rubella vaccines. • Single-dose TCV was immunogenic in 9-month-old children. • There was no safety signal related to TCV vaccination or co-administration. In 2017, the World Health Organisation (WHO) pre-qualified a single-dose typhoid conjugate vaccine (TCV) and identified TCV co-administration studies as a research priority. Accordingly, we tested co-administration of Typbar TCV® (Bharat Biotech International) with measles-rubella (MR) and yellow fever (YF) vaccines. We conducted a randomized, double-blind, and controlled, phase 2 trial in Ouagadougou, Burkina Faso. Healthy children aged 9–11 months were randomized 1:1 to receive TCV (Group 1) or control vaccine (inactivated polio vaccine (IPV), Group 2). Vaccines were administered intramuscularly with routine MR and YF vaccines. Safety was assessed by (1) local and systemic reactions on days 0, 3, and 7; (2) unsolicited adverse events within 28 days; and (3) serious adverse events (SAEs) within six months after immunization. We enrolled, randomized, and vaccinated 100 eligible children (49 Group 1 and 51 Group 2). Safety outcomes occurred with similar frequency in both groups: local/solicited reactions (Group 1: 1/49, Group 2: 3/50), systemic/solicited reactions (Group 1: 4/49, Group 2: 9/50), unsolicited adverse events (Group 1: 26/49, Group 2: 33/51), and SAEs (Group 1: 2/49, Group 2: 3/51). TCV conferred robust immunogenicity without interference with MR or YF vaccines. TCV can be safely co-administered with MR and YF vaccines to children at the 9-month vaccination visit. [ABSTRACT FROM AUTHOR]

Background & Aims: Current standard-of-care suppresses HBV replication, but does not lead to a functional cure. Treatment aiming to cure chronic hepatitis B (CHB) is believed to require the induction of strong cellular immune responses, such as by therapeutic vaccination. Methods: We designed a therapeutic HBV vaccine candidate (YF17D/HBc-C) using yellow fever vaccine YF17D as a live-attenuated vector to express HBV core antigen (HBc). Its ability to induce potent cellular immune responses was assessed in a mouse model that supports flavivirus replication. Results: Following a HBc protein prime, a booster of YF17D/HBc-C was found to induce vigorous cytotoxic T cell responses. In a direct head-to-head comparison, these HBc-specific responses exceeded those elicited by adenovirus-vectored HBc. Target-specific T cells were not only more abundant, but also showed a higher degree of polyfunctionality, with HBc-specific CD8+ T cells producing interferon γ and tumour necrosis factor α in addition to granzyme B. This immune phenotype translated into a superior cytotoxic effector activity toward HBc-positive cells in YF17D/HBc-C vaccinated animals in vivo. Conclusions: The results presented here show the potential of YF17D/HBc-C as a vaccine candidate to treat CHB, and warrant follow-up studies in preclinical animal models of HBV persistence in which other candidate vaccines have been unable to achieve a sustained virologic response. Lay summary: Resolution of CHB requires the induction of strong cellular immune responses. We used the yellow fever vaccine as a vector for HBV antigens and show that it is capable of inducing high levels of HBV-specific T cells that produce multiple cytokines simultaneously and are cytotoxic in vivo.

BackgroundYellow fever (YF) is an acute viral haemorrhagic disease prevalent in tropical Africa and Latin America. The World Health Organization (WHO) estimates that there are 200,000 cases of YF and 30,000 deaths worldwide annually. Treatment for YF is supportive, but a live attenuated virus vaccine is effective for preventing infection. WHO recommends immunisation for all individuals > 9 months living in countries or areas at risk. However, the United States Advisory Committee on Immunization Practices (ACIP) advises that YF vaccine is contraindicated in individuals with HIV. Given the large populations of HIV-infected individuals living in tropical areas where YF is endemic, YF vaccine may be an important intervention for preventing YF in immunocompromised populations.ObjectivesTo assess the risk and benefits of YF immunisation for people infected with HIV.Search methodsWe used standard Cochrane methods to search electronic databases and conference proceedings with relevant search terms without limits to language.Selection criteriaRandomised controlled trials and cohort studies of individuals with HIV infection who received YF vaccine (17DD or 17D-204).Data collection and analysisTwo authors screened abstracts of references identified by electronic or bibliographic searches according to inclusion and exclusion criteria as detailed in the protocol. We identified 199 references and examined 19 in detail for study eligibility. Data were abstracted independently using a standardised abstraction form.Main resultsThree cohort studies were included in the review. They examined 484 patients with HIV infection who received YF immunisation. Patients with HIV infection developed significantly lower concentrations of neutralising antibodies in the first year post immunisation compared to uninfected patients, though decay patterns were similar for recipients regardless of HIV infection. No study patient with HIV infection suffered serious adverse events as a result of YF vaccination.Authors' conclusionsYF vaccination can produce protective levels of neutralising antibodies in HIV patients. Immunogenicity of YF vaccine is slightly less in HIV-infected patients compared to HIV-uninfected patients. No serious adverse events related to YF vaccine were observed in HIV-infected study participants. At time of immunisation, higher CD4 cell counts and lower HIV RNA levels in patients with HIV infection seem to be key determinants for development of protective titres of neutralising antibodies. The quality of the evidence for all outcomes was low to very low. YF vaccine may potentially be used safely in HIV-infected patients, although our conclusions are limited by small numbers of patients who have been reported. To assure maximum effectiveness YF vaccine should be given to HIV-infected patients after HIV replication has been suppressed.

Infection with yellow fever virus (YFV), an explosively replicating flavivirus, results in viral hemorrhagic disease characterized by cardiovascular shock and multi-organ failure. Unvaccinated populations experience 20 to 50% fatality. Few studies have examined the pathophysiological changes that occur in humans during YFV infection due to the sporadic nature and remote locations of outbreaks. Rhesus macaques are highly susceptible to YFV infection, providing a robust animal model to investigate host-pathogen interactions. In this study, we characterized disease progression as well as alterations in immune system homeostasis, cytokine production and gene expression in rhesus macaques infected with the virulent YFV strain DakH1279 (YFV-DakH1279). Following infection, YFV-DakH1279 replicated to high titers resulting in viscerotropic disease with ∼72% mortality. Data presented in this manuscript demonstrate for the first time that lethal YFV infection results in profound lymphopenia that precedes the hallmark changes in liver enzymes and that although tissue damage was noted in liver, kidneys, and lymphoid tissues, viral antigen was only detected in the liver. These observations suggest that additional tissue damage could be due to indirect effects of viral replication. Indeed, circulating levels of several cytokines peaked shortly before euthanasia. Our study also includes the first description of YFV-DakH1279-induced changes in gene expression within peripheral blood mononuclear cells 3 days post-infection prior to any clinical signs. These data show that infection with wild type YFV-DakH1279 or live-attenuated vaccine strain YFV-17D, resulted in 765 and 46 differentially expressed genes (DEGs), respectively. DEGs detected after YFV-17D infection were mostly associated with innate immunity, whereas YFV-DakH1279 infection resulted in dysregulation of genes associated with the development of immune response, ion metabolism, and apoptosis. Therefore, WT-YFV infection is associated with significant changes in gene expression that are detectable before the onset of clinical symptoms and may influence disease progression and outcome of infection.

Abstract 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

Vaccines are formulations that equip the human immune system to fight against a pathogen. All the vaccines approved for use are safe. On vaccination, the body produces enough clonal B and T cells to resist infection. Vaccines are the most cost-effective defense against infectious diseases. In India, there are at least 19 manufactures of vaccines. In addition, there are also a large number of companies that import specific vaccine formulations and sell these in India. These include two multinational companies that have also established repacking facilities. India has a well-established Universal Immunization Program (UIP) that targets vaccination of 30 million pregnant women and 27 million newborns annually. Indian vaccines are available at affordable prices to the private consumers but are supplied free of cost to the Indian beneficiaries through the UIP. Several kinds of vaccines technology are being researched all over the world. India has concentrated on the production and supply of conventional vaccines at cost-effective prices. India is also engaged in some level of research at manufacturing companies as well as at the institutional level. Effective vaccination of pregnant women and children would translate into a generally more healthy and productive society globally. India is poised to contribute in such an endeavor.

We conducted a systematic review and a meta-analysis to assess the risk of serious adverse events in the elderly after yellow fever vaccination compared to the non-elderly population. We searched multiple databases and grey literature, and we selected research without language and publication date restrictions. Studies were analyzed in a descriptive way and meta-analyzed and expressed in terms of prevalence ratio and risk ratio with a 95% confidence interval, depending on the degree of heterogeneity found. A total of 18 studies were included and 11 were meta-analyzed. The results obtained through the meta-analysis showed a risk of serious adverse events after yellow fever vaccination three times higher for the elderly when compared to the non-elderly population and five times higher for persons > 70 years. In relation to adverse event types, viscerotropic disease associated with the yellow fever vaccine had a risk that was six times higher when compared to the population < 60 years. The evidence found supports that the vaccine indication in individuals > 60 years of age should be based on a careful analysis of individual benefit-risk assessments. The results found suggest a higher risk of events for individuals > 70 years, especially for viscerotropic and neurotropic disease associated with YFV contraindicating the use of the YFV in this age group.

ABSTRACT This observational retrospective study conducted during an yellow fever (YF) outbreak in Sao Paulo, Brazil, in 2017-2018, describes adverse events (AE) following YF vaccination of immunocompromised persons. Risks and benefits of vaccination were individually evaluated by physicians. AE were assessed by phone call or electronic mail, 14 to 90 days after vaccination. Three hundred and eighty one immunocompromised persons received a full-dose of YF vaccine. Their age ranged from 1.4 to 89.3 years (median 50.8 years); 53% were women; 178 (46.7%) had chronic kidney disease, 78 (20.5%) had immune-mediated inflammatory diseases; 94 (24.7%) were using or had recently used immunosuppressive/ immunomodulatory drugs. All of them denied previous YF vaccination. We were able to contact 341 (89.5%) vaccinees: 233 (68.3%) of them received the YF vaccine from BioManguinhos and 108 (31.7%) received the vaccine from Sanofi-Pasteur; 130 (38.1%) vaccinees received other vaccines (up to 4) simultaneously with the the YF vaccine, mostly hepatitis B (59 vaccinees), pneumococcal polysaccharide 23-valent (46), influenza (43) and diphtheria-tetanus (dT, 41). One hundred and eleven vaccinees (32.6%) reported at least one AE: 79 (23.2%) presented systemic AE, 44 (12.9%) had local AE and 12 had both, local and systemic AE. The most common AE was pain at the injection site (41 persons, 12%), myalgia (34; 10%), fever (25; 7.3%) and headache (16; 4.7%). There was no statistically significant difference on the AE frequency according to the vaccine producer. There were four severe AE: one hospitalization and three deaths, considered not related to the YF vaccine.

• vYF-247 was cloned from YF-VAX and adapted for growth in serum-free Vero cells. • vYF-247 selected by safety/immunogenicity/efficacy criteria in small animal models. • vYF-247 was less neurovirulent than Stamaril and YF-VAX. • vYF-247 had similar attenuation profile, viscerotropism, neurotropism and immunogenicity to YF-VAX. • vYF-247 protects hamsters from lethal challenge with yellow fever Jimenez P10 virus. Yellow fever (YF) remains a threat to human health in tropical regions of Africa and South America. Live-attenuated YF-17D vaccines have proven to be safe and effective in protecting travellers and populations in endemic regions against YF, despite very rare severe reactions following vaccination — YF vaccine-associated viscerotropic disease (YEL-AVD) and neurological disease (YEL-AND). We describe the generation and selection of a live-attenuated YF-17D vaccine candidate and present its preclinical profile. Initially, 24 YF-17D vaccine candidate sub-strains from the Stamaril® and YF-VAX® lineage were created through transfection of viral genomic RNA into Vero cells cultured in serum-free media to produce seed lots. The clone with the 'optimal' preclinical profile, i.e. the lowest neurovirulence, neurotropism and viscerotropism, and immunogenicity at least comparable with Stamaril and YF-VAX in relevant animal models, was selected as the vaccine candidate and taken forward for assessment at various production stages. The 'optimal' vaccine candidate was obtained from the YF-VAX lineage (hence named vYF-247) and had five nucleotide differences relative to its parent, with only two changes that resulted in amino acid changes at position 480 of the envelope protein (E) (valine to leucine), and position 65 of the non-structural protein 2A (NS2A) (methionine to valine). vYF-247 was less neurovirulent in mice than Stamaril and YF-VAX irrespective of production stage. Its attenuation profile in terms of neurotropism and viscerotropism was similar to YF-VAX in A129 mice, a 'worst case' animal model lacking type-I IFN receptors required to initiate viral clearance. Thus, vYF-247 would not be expected to have higher rates of YEL-AVD or YEL-AND than Stamaril and YF-VAX. In hamsters, vYF-247 was immunogenic and protected against high viremia and death induced by a lethal challenge with the hamster-adapted Jimenez P10 YF virus strain. Our data suggests that vYF-247 would provide robust protection against YF disease in humans, similar to currently marketed YF vaccines. [ABSTRACT FROM AUTHOR]

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

This observational retrospective study conducted during an yellow fever (YF) outbreak in Sao Paulo, Brazil, in 2017-2018, describes adverse events (AE) following YF vaccination of immunocompromised persons. Risks and benefits of vaccination were individually evaluated by physicians. AE were assessed by phone call or electronic mail, 14 to 90 days after vaccination. Three hundred and eighty one immunocompromised persons received a full-dose of YF vaccine. Their age ranged from 1.4 to 89.3 years (median 50.8 years); 53% were women; 178 (46.7%) had chronic kidney disease, 78 (20.5%) had immune-mediated inflammatory diseases; 94 (24.7%) were using or had recently used immunosuppressive/immunomodulatory drugs. All of them denied previous YF vaccination. We were able to contact 341 (89.5%) vaccinees: 233 (68.3%) of them received the YF vaccine from BioManguinhos and 108 (31.7%) received the vaccine from Sanofi-Pasteur; 130 (38.1%) vaccinees received other vaccines (up to 4) simultaneously with the the YF vaccine, mostly hepatitis B (59 vaccinees), pneumococcal polysaccharide 23-valent (46), influenza (43) and diphtheria-tetanus (dT, 41). One hundred and eleven vaccinees (32.6%) reported at least one AE: 79 (23.2%) presented systemic AE, 44 (12.9%) had local AE and 12 had both, local and systemic AE. The most common AE was pain at the injection site (41 persons, 12%), myalgia (34; 10%), fever (25; 7.3%) and headache (16; 4.7%). There was no statistically significant difference on the AE frequency according to the vaccine producer. There were four severe AE: one hospitalization and three deaths, considered not related to the YF vaccine. [ABSTRACT FROM AUTHOR]

Rationale: The effectiveness of immunisation with pneumococcal conjugate vaccine (PCV) has been demonstrated in many countries. However, the global impact of PCV is limited by its cost, which has prevented its introduction in some countries. Reducing the cost of PCV programmes will facilitate further vaccine introductions and improve the sustainability of PCV in low-income countries when they transition from subsidised vaccine supply. We are conducting a large, population-level, cluster-randomised field trial (PVS) of an alternative reduced-dose schedule of PCV compared to the standard schedule. We are also conducting a nested sub-study at the individual level to investigate the immunogenicity of the two schedules and their effects on pneumococcal carriage acquisition (PVS-AcqImm)., Methods and Design: PVS-AcqImm is a prospective, cluster-randomised trial of an alternative schedule of one dose of PCV scheduled at age 6 weeks with a booster dose at age 9 months compared to the standard of three primary doses scheduled at 6, 10, and 14 weeks of age. Sub-groups within the alternative schedule group receive yellow fever vaccine separately or co-administered with PCV at 9 months of age. The primary endpoints are (a) concentrations of vaccine-type anti-pneumococcal IgG at 18 months of age, (b) proportions with yellow fever neutralising antibody titre ≥ 1:8 4 weeks after separate or co-administration of PCV and yellow fever vaccines, and (c) rate of nasopharyngeal vaccine-type pneumococcal acquisition from 10-14 months of age. Participants and field staff are not masked to group allocation while measurement of the laboratory endpoints is masked. Approximately equal numbers of participants are resident in each of 28 randomly allocated geographic clusters (14 clusters in each group); 784 enrolled for acquisition measurements and 336 for immunogenicity measurements., Purpose: This statistical analysis plan (SAP) describes the PVS-AcqImm cohort and follow-up criteria to be used in different analyses. The SAP defines the endpoints and describes how adherence to the interventions will be presented. We describe the approach to analyses and how we will account for the effect of clustering. Defining the SAP prior to the conduct of analysis will avoid bias in analyses that may arise from prior knowledge of trial findings., Trial Registration: ISRCTN, ISRCTN7282161328. Registered on 28 November 2019. https://www.isrctn.com/ISRCTN72821613 ., Protocol: MRCG SCC number 1670, LSHTM Ref 17683. Current protocol version: 6.0, 24 May 2021. Version: 1.0 (5 April 2023); SAP revisions-none., (© 2024. The Author(s).)

Background: Live attenuated vaccines alter immune functions and are associated with beneficial outcomes. We previously demonstrated that live attenuated yellow fever virus (YFV) vaccine (LA-YF-Vax) dampens T-cell receptor (TCR) signaling in vitro via an RNA-based mechanism. We examined study participants before and after LA-YF-Vax to assess TCR-mediated functions in vivo., Methods: Serum samples and peripheral blood mononuclear cells (PBMCs) were obtained before and after LA-YF-Vax (with or without additional vaccines) or quadrivalent influenza vaccine. TCR-mediated activation was determined by interleukin 2 release or phosphorylation of the lymphocyte-specific Src kinase. TCR-regulating phosphatase (protein tyrosine phosphatase receptor type E [PTPRE]) expression was also measured., Results: Compared with prevaccination findings, LA-YF-Vax recipient PBMCs demonstrated transient reduction in interleukin 2 release after TCR stimulation and PTPRE levels, unlike in control participants who received quadrivalent influenza vaccine. YFV was detected in 8 of 14 participants after LA-YF-Vax. After incubation of healthy donor PBMCs in serum-derived extracellular vesicles prepared from LA-YF-Vax recipients, TCR signaling and PTPRE levels were reduced after vaccination, even in participants without detectable YFV RNA., Conclusions: LA-YF-Vax reduces TCR functions and PTPRE levels after vaccination. Extracellular vesicles from serum recapitulated this effect in healthy cells. This likely contributes to the reduced immunogenicity for heterologous vaccines after LA-YF-Vax administration. Identification of specific immune mechanisms related to vaccines should contribute to understanding of the "off-target," beneficial effects of live vaccines., Competing Interests: Potential conflicts of interest . All authors: No reported conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (Published by Oxford University Press on behalf of Infectious Diseases Society of America 2023.)

The yellow fever 17D vaccine (YF17D) is highly effective but is frequently administered to individuals with pre-existing cross-reactive immunity, potentially impacting their immune responses. Here, we investigate the impact of pre-existing flavivirus immunity induced by the tick-borne encephalitis virus (TBEV) vaccine on the response to YF17D vaccination in 250 individuals up to 28 days post-vaccination (pv) and 22 individuals sampled one-year pv. Our findings indicate that previous TBEV vaccination does not affect the early IgM-driven neutralizing response to YF17D. However, pre-vaccination sera enhance YF17D virus infection in vitro via antibody-dependent enhancement (ADE). Following YF17D vaccination, TBEV-pre-vaccinated individuals develop high amounts of cross-reactive IgG antibodies with poor neutralizing capacity. In contrast, TBEV-unvaccinated individuals elicit a non-cross-reacting neutralizing response. Using YF17D envelope protein mutants displaying different epitopes, we identify quaternary dimeric epitopes as the primary target of neutralizing antibodies. Additionally, TBEV-pre-vaccination skews the IgG response towards the pan-flavivirus fusion loop epitope (FLE), capable of mediating ADE of dengue and Zika virus infections in vitro. Together, we propose that YF17D vaccination conceals the FLE in individuals without prior flavivirus exposure but favors a cross-reactive IgG response in TBEV-pre-vaccinated recipients directed to the FLE with potential to enhance dengue virus infection., (© 2024. The Author(s).)

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., Competing Interests: Conflicts of interest The authors declare no conflicts of interest., (Copyright © 2024 Sociedade Brasileira de Infectologia. Published by Elsevier España, S.L.U. All rights reserved.)