Persistence of Neutralizing Antibody Responses Among Yellow Fever Virus 17D Vaccinees Living in a Nonendemic Setting

Long-term immunity following yellow fever vaccination: a systematic review and meta-analysis

BACKGROUND

Long-term immunity following yellow fever vaccination remains controversial. We aimed to summarise the literature regarding the long-term protection (≥10 years) conveyed by a single dose of yellow fever vaccination.

METHODS

In this systematic review and meta-analysis, we searched 11 databases from database inception to Aug 24, 2023. We included cohort and cross-sectional studies reporting immunogenicity outcomes for children or adults who received a single dose of yellow fever vaccination 10 or more years ago. Case series and single case reports were excluded. Participants who received more than one dose of yellow fever vaccination before measurement of the outcome were excluded. Identified records were reviewed by two independent reviewers. The primary outcome of the meta-analysis was the pooled seroprotection rate. Risk of bias was assessed with the Risk Of Bias In Non-randomized Studies of Interventions tool, and the Joanna Briggs Institute tool for analytical cross-sectional studies. Studies of moderate or good quality that reported seroprotection were included for random-effects meta-analysis and stratified by endemicity and specific risk groups. The study was registered with PROSPERO, CRD42023384087.

FINDINGS

Of the 7363 articles identified by our search, 39 were eligible for inclusion for systematic review. These studies comprised 2895 individuals vaccinated 10-60 years ago. 20 studies were included in the meta-analysis. Pooled seroprotection rates were 94% (95% CI 86-99) among healthy adults in a non-endemic setting (mostly travellers) and 76% (65-85) in an endemic setting (all Brazilian studies). The pooled seroprotection rate was 47% (35-60) in children (aged 9-23 months at time of vaccination) and 61% (38-82) in people living with HIV. Reported criteria for seroprotection were highly heterogeneous.

INTERPRETATION

The gathered evidence suggests that a single dose of yellow fever vaccination provides lifelong protection in travellers. However, in people living with HIV and children (younger than 2 years), booster doses might still be required because lower proportions of vaccinees were seroprotected 10 or more years post-vaccination. Lower observed seroprotection rates among residents of endemic areas were partly explained by the use of a higher cutoff for seroprotection that was applied in Brazil. Studies from sub-Saharan Africa were scarce and of low quality; thus no conclusions could be drawn for this region.

FUNDING

None.

In silico design and evaluation of a novel mRNA vaccine against BK virus: a reverse vaccinology approach

Human polyomavirus type 1, or BK virus (BKV), is a ubiquitous pathogen belonging to the polyomaviridae family mostly known for causing BKV-associated nephropathy (BKVN) and allograft rejection in kidney transplant recipients (KTRs) following the immunosuppression regimens recommended in these patients. Reduction of the immunosuppression level and anti-viral agents are the usual approaches for BKV clearance, which have not met a desired outcome yet. There are also debating matters such as the effect of this pathogen on emerging various comorbidities and the related malignancies in the human population. In this study, a reverse vaccinology approach was implemented to design a mRNA vaccine against BKV by identifying the most antigenic proteins of this pathogen. Potential immunogenic T and B lymphocyte epitopes were predicted through various immunoinformatic tools. The final epitopes were selected according to antigenicity, toxicity, allergenicity, and cytokine inducibility scores. According to the obtained results, the designed vaccine was antigenic, neutral at the physiological pH, non-toxic, and non-allergenic with a world population coverage of 93.77%. Since the mRNA codon optimization ensures the efficient expression of the vaccine in a host cell, evaluation of different parameters showed our designed mRNA vaccine has a stable structure. Moreover, it had strong interactions with toll-like receptor 4 (TLR4) according to the molecular dynamic simulation studies. The in silico immune simulation analyses revealed an overall increase in the immune responses following repeated exposure to the designed vaccine. Based on our findings, the vaccine candidate is ready to be tested as a promising novel mRNA therapeutic vaccine against BKV.

Duration of Protection After Vaccination Against Yellow Fever: A Systematic Review and Meta-Analysis

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.

Supplying the trip to antibody production-nutrients, signaling, and the programming of cellular metabolism in the mature B lineage

The COVID pandemic has refreshed and expanded recognition of the vital role that sustained antibody (Ab) secretion plays in our immune defenses against microbes and of the importance of vaccines that elicit Ab protection against infection. With this backdrop, it is especially timely to review aspects of the molecular programming that govern how the cells that secrete Abs arise, persist, and meet the challenge of secreting vast amounts of these glycoproteins. Whereas plasmablasts and plasma cells (PCs) are the primary sources of secreted Abs, the process leading to the existence of these cell types starts with naive B lymphocytes that proliferate and differentiate toward several potential fates. At each step, cells reside in specific microenvironments in which they not only receive signals from cytokines and other cell surface receptors but also draw on the interstitium for nutrients. Nutrients in turn influence flux through intermediary metabolism and sensor enzymes that regulate gene transcription, translation, and metabolism. This review will focus on nutrient supply and how sensor mechanisms influence distinct cellular stages that lead to PCs and their adaptations as factories dedicated to Ab secretion. Salient findings of this group and others, sometimes exhibiting differences, will be summarized with regard to the journey to a distinctive metabolic program in PCs.

Dengue and Zika virus infections in children elicit cross-reactive protective and enhancing antibodies that persist long term

[Figure: see text].

Re-emergence of yellow fever in the neotropics - quo vadis?

Yellow fever virus (YFV) is the etiological agent of yellow fever (YF), an acute hemorrhagic vector-borne disease with a significant impact on public health, is endemic across tropical regions in Africa and South America. The virus is maintained in two ecologically and evolutionary distinct transmission cycles: an enzootic, sylvatic cycle, where the virus circulates between arboreal Aedes species mosquitoes and non-human primates, and a human or urban cycle, between humans and anthropophilic Aedes aegypti mosquitoes. While the urban transmission cycle has been eradicated by a highly efficacious licensed vaccine, the enzootic transmission cycle is not amenable to control interventions, leading to recurrent epizootics and spillover outbreaks into human populations. The nature of YF transmission dynamics is multifactorial and encompasses a complex system of biotic, abiotic, and anthropogenic factors rendering predictions of emergence highly speculative. The recent outbreaks in Africa and Brazil clearly remind us of the significant impact YF emergence events pose on human and animal health. The magnitude of the Brazilian outbreak and spillover in densely populated areas outside the recommended vaccination coverage areas raised the specter of human — to — human transmission and re-establishment of enzootic cycles outside the Amazon basin. Herein, we review the factors that influence the re-emergence potential of YFV in the neotropics and offer insights for a constellation of coordinated approaches to better predict and control future YF emergence events.

The COVID-19 Vaccine Landscape

The history of vaccine development spans centuries. At first, whole pathogens were used as vaccine agents, either inactivated or attenuated, to reduce virulence in humans. Safety and tolerability were increased by including only specific proteins as antigens and using cell culture methods, while novel vaccine strategies, like nucleic acid- or vector-based vaccines, hold high promise for the future. Vaccines have generally not been employed as the primary tools in outbreak response, but this might change since advances in medical technology in the last decades have made the concept of developing vaccines against novel pathogens a realistic strategy. Wandering the uncharted territory of a novel pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), we can learn from other human Betacoronaviridae that emerged in the last decades, SARS-CoV-1 and MERS-CoV. We can identify the most likely target structures of immunity, establish animal models that emulate human disease and immunity as closely as possible, and learn about complex mechanisms of immune interaction such as cross-reactivity or antibody-dependent enhancement (ADE). However, significant knowledge gaps remain. What are the correlates of protection? How do we best induce immunity in vulnerable populations like the elderly? Will the immunity induced by vaccination (or by natural infection) wane over time? To date, at least 149 vaccine candidates against SARS-CoV-2 are under development. At the time of writing, at least 17 candidates have already progressed past preclinical studies (in vitro models and in vivo animal experiments) into clinical development. This chapter will provide an overview of this rapidly developing field.

Vaccination and Therapeutics: Responding to the Changing Epidemiology of Yellow Fever

At the turn of the nineteenth century, yellow fever (YF) was considered the most dangerous infectious disease with high case fatality. Subsequent, mass vaccination campaigns coupled with widespread elimination of the YF mosquito vector significantly decreased YF cases and reduced outbreaks to the tropical and subtropical forested regions of Africa and South America. However, recent (2016) large outbreaks in Angola, Democratic Republic of Congo (DRC), and South-Eastern Brazil, where previously had been demarcated as low-risk regions, have highlighted the possibility of a rapidly changing epidemiology and the potential re-emergence of yellow fever virus (YFV). Furthermore, the first-ever importation of YFV into Asia has highlighted the potential fear of YFV emerging as a global threat. In this review, we describe the changing epidemiology of YF outbreaks, and highlight the use of public health policies, therapeutics, and vaccination as tools to help eliminate future YFV outbreaks.

Safety and immunogenicity of a primary yellow fever vaccination under low-dose methotrexate therapy-a prospective multi-centre pilot study1

BACKGROUND

More people on immunosuppression live in or wish to travel to yellow fever virus (YFV)-endemic areas. Data on the safety and immunogenicity of yellow fever vaccination (YFVV) during immunosuppression are scarce. The aim of this study was to compare the safety and immunogenicity of a primary YFVV between travellers on methotrexate and controls.

METHODS

We conducted a prospective multi-centre controlled observational study from 2015 to 2017 in six Swiss travel clinics. 15 adults (nine with rheumatic diseases, five with dermatologic conditions and one with a gastroenterological disease) on low-dose methotrexate (≤20 mg/week) requiring a primary YFVV and 15 age and sex-matched controls received a YFVV. Solicited/unsolicited adverse reactions were recorded, YFV-RNA was measured in serum samples on Days 3, 7, 10, 14, 28 and neutralizing antibodies on Days 0, 7, 10, 14, 28.

RESULTS

Patients´ and controls' median ages were 53 and 52 years; 9 patients and 10 controls were female. 43% of patients and 33% of controls showed local side effects (P = 0.71); 86% of patients and 66% of controls reported systemic reactions (P = 0.39). YFV-RNA was detected in patients and controls on Day 3-10 post-vaccination and was never of clinical significance. Slightly more patients developed YFV-RNAaemia (Day 3: n = 5 vs n = 2, Day 7: n = 9 vs n = 7, Day 10: n = 3 vs n = 2, all P > 0.39). No serious reactions occurred. On Day 10, a minority of vaccinees was seroprotected (patients: n = 2, controls: n = 6). On Day 28, all vaccinees were seroprotected.

CONCLUSIONS

First-time YFVV was safe and immunogenic in travellers on low-dose methotrexate. Larger studies are needed to confirm these promising results.

Vaccination and Therapeutics: Responding to the Changing Epidemiology of Yellow Fever

Purpose of Review

At the turn of the nineteenth century, yellow fever (YF) was considered the most dangerous infectious disease with high case fatality. Subsequent, mass vaccination campaigns coupled with widespread elimination of the YF mosquito vector significantly decreased YF cases and reduced outbreaks to the tropical and subtropical forested regions of Africa and South America.

Recent Findings

However, recent (2016) large outbreaks in Angola, Democratic Republic of Congo (DRC), and South-Eastern Brazil, where previously had been demarcated as low-risk regions, have highlighted the possibility of a rapidly changing epidemiology and the potential re-emergence of yellow fever virus (YFV). Furthermore, the first-ever importation of YFV into Asia has highlighted the potential fear of YFV emerging as a global threat.

Summary

In this review, we describe the changing epidemiology of YF outbreaks and highlight the use of public health policies, therapeutics, and vaccination as tools to help eliminate future YFV outbreaks.

Review of data and knowledge gaps regarding yellow fever vaccine-induced immunity and duration of protection

Yellow fever (YF) virus is a mosquito-borne flavivirus found in Sub-Saharan Africa and tropical South America. The virus causes YF, a viral hemorrhagic fever, which can be prevented by a live-attenuated vaccine, strain 17D. Despite the vaccine being very successful at decreasing disease risk, YF is considered a re-emerging disease due to the increased numbers of cases in the last 30 years. Until 2014, the vaccine was recommended to be administered with boosters every 10 years, but in 2014 the World Health Organization recommended removal of booster doses for all except special populations. This recommendation has been questioned and there have been reports of waning antibody titers in adults over time and more recently in pediatric populations. Clearly, the potential of waning antibody titers is a very important issue that needs to be carefully evaluated. In this Perspective, we review what is known about the correlate of protection for full-dose YF vaccine, current information on waning antibody titers, and gaps in knowledge. Overall, fundamental questions exist on the durability of protective immunity induced by YF vaccine, but interpretation of studies is complicated by the use of different assays and different cut-offs to measure seroprotective immunity, and differing results among certain endemic versus non-endemic populations. Notwithstanding the above, there are few well-characterized reports of vaccine failures, which one would expect to observe potentially more with the re-emergence of a severe disease. Overall, there is a need to improve YF disease surveillance, increase primary vaccination coverage rates in at-risk populations, and expand our understanding of the mechanism of protection of YF vaccine.

Designing a novel mRNA vaccine against SARS-CoV-2: An immunoinformatics approach

SARS-CoV-2 is the deadly virus behind COVID-19, the disease that went on to ravage the world and caused the biggest pandemic 21st century has witnessed so far. On the face of ongoing death and destruction, the urgent need for the discovery of a vaccine against the virus is paramount. This study resorted to the emerging discipline of immunoinformatics in order to design a multi-epitope mRNA vaccine against the spike glycoprotein of SARS-CoV-2. Various immunoinformatics tools were utilized to predict T and B lymphocyte epitopes. The epitopes were channeled through a filtering pipeline comprised of antigenicity, toxicity, allergenicity, and cytokine inducibility evaluation with the goal of selecting epitopes capable of generating both T and B cell-mediated immune responses. Molecular docking simulation between the epitopes and their corresponding MHC molecules was carried out. 13 epitopes, a highly immunogenic adjuvant, elements for proper sub-cellular trafficking, a secretion booster, and appropriate linkers were combined for constructing the vaccine. The vaccine was found to be antigenic, almost neutral at physiological pH, non-toxic, non-allergenic, capable of generating a robust immune response and had a decent worldwide population coverage. Based on these parameters, this design can be considered a promising choice for a vaccine against SARS-CoV-2.

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SARS-CoV-2, the causative agent for COVID-19, has caused the biggest pandemic 21st century has witnessed so far.

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Here, immunoinformatics was used for designing a muti-epitope mRNA vaccine against the spike glycoprotein of SARS-CoV-2.

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Through stringent selection of T and B cell epitopes and other necessary elements, a vaccine was constructed in silico.

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Proposed mechanism of its synthesis, delivery and action has also been presented.

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The vaccine was found to be immunogenic, almost neutral, non-toxic, non-allergenic and has a decent worldwide coverage.

Yellow fever control: current epidemiology and vaccination strategies

Yellow fever (YF) outbreaks continue, have expanded into new areas and threaten large populations in South America and Africa. Predicting where epidemics might occur must take into account local mosquito populations and specific YF virus strain, as well as ecoclimatic conditions, sociopolitical and demographic factors including population size, density, and mobility, and vaccine coverage. Populations of Aedes aegypti and Aedes albopictus from different regions vary in susceptibility to and capacity to transmit YF virus. YF virus cannot be eliminated today because the virus circulates in animal reservoirs, but human disease could be eliminated with wide use of the vaccine. WHO EYE (Eliminate Yellow Fever Epidemics) is a welcome plan to control YF, with strategies to be carried out from 2017 to 2026: to expand use of YF vaccine, to prevent international spread, and to contain outbreaks rapidly. YF vaccination is the mainstay in controlling YF outbreaks, but global supply is insufficient. Therefore, dose-sparing strategies have been proposed including fractional dosing and intradermal administration. Fractional dosing has been effectively used in outbreak control but currently does not satisfy International Health Regulations; special documentation is needed for international travel. Vector control is another facet in preventing YF outbreaks, and novel methods are being considered and proposed.