Ebola Hemorrhagic Fever and the Current State of Vaccine Development

Current Ebola virus outbreak in West Africa already reached the total number of 1,323 including 729 deaths by July 31st. the fatality is around 55% in the southeastern area of Guinea, Sierra Leone, Liberia, and Nigeria. The number of patients with Ebola Hemorrhagic Fever (EHF) was continuously increasing even though the any effective therapeutics or vaccines has not been developed yet. The Ebola virus in Guinea showed 98% homology with Zaire Ebola Virus.Study of the pathogenesis of Ebola virus infection and assess of the various candidates of vaccine have been tried for a long time, especially in United States and some European countries. Even though the attenuated live vaccine and DNA vaccine containing Ebola viral genes were tested and showed efficacy in chimpanzees, those candidates still need clinical tests requiring much longer time than the preclinical development to be approved for the practical treatment.It can be expected to eradicate Ebola virus by a safe and efficient vaccine development similar to the case of smallpox virus which was extinguished from the world by the variola vaccine.     

Third-generation smallpox vaccine strain-based recombinant vaccines for viral hemorrhagic fevers

Vaccinia virus has been used as a smallpox vaccine. Now that smallpox has been eradicated, the vaccinia virus is expected to be used as a bioterrorism countermeasure and a recombinant vaccine vector for other infectious diseases, such as viral hemorrhagic fevers. Many vaccinia virus strains were used as smallpox vaccines in the smallpox eradication campaign coordinated by the World Health Organization. These strains can be classified into generations, according to the history of improving production methods and efforts to reduce the adverse reactions. Significantly, the third-generation of smallpox vaccine strains, which include modified vaccinia Ankara (MVA) and LC16m8, are currently popular as recombinant vaccine vectors due to their well-balanced safety and immunogenicity profiles. The present review firstly focuses on the characteristics of the smallpox vaccine generations. The historical background of the development of the third-generation smallpox vaccine strains is detailed, along with the history of the transition of the vaccinia virus generation used as vectors for hemorrhagic fever vaccines to the third generation. Among the vaccinia viruses, MVA is currently the most commonly used vector for developing hemorrhagic fever vaccines, including dengue fever, yellow fever, Ebola viral disease, Lassa fever, Rift Valley fever, and Crimean-Congo hemorrhagic fever. LC16m8 is a vaccine candidate for severe fever with thrombocytopenia syndrome. The current status and recent advances in the development of these hemorrhagic fever vaccines using third-generation vaccinia strains are discussed.     

Safety of Recombinant VSV–Ebola Virus Vaccine Vector in Pigs

The ongoing Ebola outbreak in West Africa has resulted in fast-track development of vaccine candidates. We tested a vesicular stomatitis virus vector expressing Ebola virus glycoprotein for safety in pigs. Inoculation did not cause disease and vaccine virus shedding was minimal, which indicated that the vaccine virus does not pose a risk of dissemination in pigs.     

埃博拉病毒包膜糖蛋白研究进展

埃博拉出血热是新现传染病，死亡率高，其病原体为埃博拉病毒，目前对其致病机制还未明了，而且还没有有效的疫苗预防。该文就埃博拉病毒糖蛋白的分子生物学特征、致病机制以及疫苗的研究进展作一综述。     

Factors contributing to and strategies to combat emerging arboviruses

ABSTRACT

Less than half a century ago infectious diseases appeared to be destined to be extinguished via as a culmination of medical triumphs. As focus turned towards combating non-communicable diseases, emerging and re-emerging diseases (EIDs) have bloomed from those ashes. Five epidemic mosquito-borne arboviruses (Yellow Fever virus (YFV), Dengue virus, West Nile virus, Chikungunya virus, and Zika virus) have emerged in the recent past. Arboviruses are of the utmost importance with respect to EIDs due to intensive growth of globalisation, arthropod urban fitness/adaption, and environmental changes. We focus on recent outbreaks of the arthropod borne viruses (arboviruses) Zika virus and YFV. Factors contributing to the blossoming of EIDs (environmental, globalisation, and urbanisation) and combating strategies (surveillance, containment, and prevention) will be discussed. Specifically, Zika virus and YFV will be used in the context of these factors and strategies. YFV is discussed in detail as it pertains to these factors and strategies in the United States (US), 2017 Brazil Outbreak, 2016 Africa Outbreak, and global risk. Vigilance is needed to focus on, prevent, and control the current and next arbovirus EIDs.     

Cytotoxic T lymphocytes to Ebola Zaire virus are induced in mice by immunization with liposomes containing lipid A

An eight amino acid sequence (TELRTFSI) present in the carboxy terminal end (aa 577-584) of membrane-anchored GP, the major structural protein of Ebola virus, was identified as an H-2k-specific murine cytotoxic T cell epitope. Cytotoxic T lymphocytes (CTLs) to this epitope were induced by immunizing B10.BR mice intravenously with either irradiated Ebola virus or with irradiated Ebola virus encapsulated in liposomes containing lipid A. The CTL response induced by irradiated Ebola virus could not be sustained after the second round of in vitro stimulation of immune splenocytes with the peptide, unless the irradiated virus was encapsulated in liposomes containing lipid A. The identification of an Ebola GP-specific CTL epitope and the requirement of liposomal lipid A for CTL memory recall responses could prove to be a promising approach for developing a vaccine against Ebola virus infection.     

Skepticism toward Emerging Infectious Diseases and Influenza Vaccination Intentions in Nurses

Nurses generally show low compliance with vaccination recommendations. We assessed whether low vaccine acceptance is due to skeptical attitudes toward emerging infectious diseases (EIDs). Skepticism toward EIDs manifests as doubts about the real threat of emerging diseases and as distrust in the motives and the competence of institutions that fight these diseases. We performed a cross-sectional questionnaire study in 293 Swiss nurses using a newly developed scale to assess skepticism toward EIDs. Skepticism affected nurses’ intentions to vaccinate themselves against seasonal influenza and against possible future pandemic influenza. The influence of skepticism persisted after controlling for other factors that are known to determine nurses’ vaccination behavior, namely vaccination habits, feeling at risk of catching influenza, and perceiving vaccination as a professional duty. Skeptical attitudes toward EIDs seem to have a unique and hitherto ignored impact on vaccination intentions. Nurses’ vaccine acceptance could be increased if vaccination campaigns specifically target skeptical attitudes toward EIDs. These campaigns should address nurses’ doubts about the real threat of EIDs and should rebuild their trust in institutions which fight these diseases.     

Towards quantification of protective antibody responses by passive transfer of the 1st WHO International Standard for Ebola virus antibody in a guinea pig model

Ebola virus (EBOV) represents a major concern to global health due to the unpredictable nature of outbreaks. Infection with EBOV can cause a severe viral haemorrhagic fever with no licensed vaccine or treatment, restricting work with live EBOV to Containment/Biosafety Level 4 facilities. Whilst the magnitude of recent outbreaks has provided an impetus for vaccine and antiviral development, establishing the efficacy of candidate vaccine materials relies on EBOV challenge models and advanced human trials should outbreaks occur and where logistics and funding allow. To address these hurdles in vaccine development, we investigated whether a recently established serological reference standard, the 1st WHO International Standard for Ebola virus antibody, could be used to provide a quantifiable correlate of immune protection in vivo. Dilutions of the International Standard were inoculated into naïve guinea pigs 24 h before challenge with a lethal dose of Ebola virus. Only subjects receiving the highest dose of the International Standard exhibited evidence of delayed progression. Due to it being a WHO established reagent and available globally upon request, this standard allows for effective comparisons of data between laboratories and may prove valuable to select the candidate vaccines that are most likely to confer humoral immune protection ensuring the most promising candidates progress into efficacy studies.     

Considerations for use of Ebola vaccine during an emergency response

Vaccination against Ebola virus disease is a tool that may limit disease transmission and deaths in future outbreaks, integrated within traditional Ebola outbreak prevention and control measures. Although a licensed Ebolavirus vaccine (EV) is not yet available, the 2014–2016 West African Ebola outbreak has accelerated EV clinical trials and given public health authorities in Guinea, Liberia, and Sierra Leone experience with implementation of emergency ring vaccination. As evidence supporting the use of EV during an outbreak response has become available, public health authorities in at-risk countries are considering how to integrate EV into future emergency Ebola responses and for prevention in high-risk groups, such as healthcare workers and frontline workers (HCW/FLWs), even before an EV is licensed. This review provides an overview of Ebola epidemiology, immunology, and evidence to inform regional and country-level decisions regarding EV delivery during an emergency response and to at-risk populations before a licensed vaccine is available and beyond. Countries or regions planning to use EV will need to assess factors such as the likelihood of a future Ebolavirus outbreak, the most likely species to cause an outbreak, the availability of a safe and effective EV (unlicensed or licensed) for the affected population, capacity to implement Ebola vaccination in conjunction with standard Ebola outbreak control measures, and availability of minimum essential resources and regulatory requirements to implement emergency Ebola vaccination. Potential emergency vaccination strategies for consideration include ring or geographically targeted community vaccination, HCW/FLW vaccination, and mass vaccination. The development of guidelines and protocols for Ebola vaccination will help ensure that activities are standardized, evidence-based, and well-coordinated with overall Ebola outbreak response efforts in the future.     

Vesicular Stomatitis Virus–Based Vaccines against Lassa and Ebola Viruses

We demonstrated that previous vaccination with a vesicular stomatitis virus (VSV)–based Lassa virus vaccine does not alter protective efficacy of subsequent vaccination with a VSV-based Ebola virus vaccine. These findings demonstrate the utility of VSV-based vaccines against divergent viral pathogens, even when preexisting immunity to the vaccine vector is present.     

Ebola virus glycoprotein Fc fusion protein confers protection against lethal challenge in vaccinated mice

Ebola virus is a Filoviridae that causes hemorrhagic fever in humans and induces high morbidity and mortality rates. Filoviruses are classified as “Category A bioterrorism agents”, and currently there are no licensed therapeutics or vaccines to treat and prevent infection. The Filovirus glycoprotein (GP) is sufficient to protect individuals against infection, and several vaccines based on GP are under development including recombinant adenovirus, parainfluenza virus, Venezuelan equine encephalitis virus, vesicular stomatitis virus (VSV) and virus-like particles. Here we describe the development of a GP Fc fusion protein as a vaccine candidate. We expressed the extracellular domain of the Zaire Ebola virus (ZEBOV) GP fused to the Fc fragment of human IgG1 (ZEBOVGP-Fc) in mammalian cells and showed that GP undergoes the complex furin cleavage and processing observed in the native membrane-bound GP. Mice immunized with ZEBOVGP-Fc developed T-cell immunity against ZEBOV GP and neutralizing antibodies against replication-competent VSV-G deleted recombinant VSV containing ZEBOV GP. The ZEBOVGP-Fc vaccinated mice were protected against challenge with a lethal dose of ZEBOV. These results show that vaccination with the ZEBOVGP-Fc fusion protein alone without the need of a viral vector or assembly into virus-like particles is sufficient to induce protective immunity against ZEBOV in mice. Our data suggested that Filovirus GP Fc fusion proteins could be developed as a simple, safe, efficacious, and cost effective vaccine against Filovirus infection for human use.     

A cytomegalovirus-based vaccine provides long-lasting protection against lethal Ebola virus challenge after a single dose

Ebola virus (Zaire ebolavirus; EBOV) is a highly lethal hemorrhagic disease virus that most recently was responsible for two independent 2014 outbreaks in multiple countries in Western Africa, and the Democratic Republic of the Congo, respectively. Herein, we show that a cytomegalovirus (CMV)-based vaccine provides durable protective immunity from Ebola virus following a single vaccine dose. This study has implications for human vaccination against ebolaviruses, as well as for development of a ‘disseminating’ vaccine to target these viruses in wild African great apes.     

Effect of Recombinant Vesicular Stomatitis Virus–Zaire Ebola Virus Vaccination on Ebola Virus Disease Illness and Death,Democratic Republic of the Congo

We conducted a retrospective cohort study to assess the effect vaccination with the live-attenuated recombinant vesicular stomatitis virus–Zaire Ebola virus vaccine had on deaths among patients who had laboratory-confirmed Ebola virus disease (EVD). We included EVD-positive patients coming to an Ebola Treatment Center in eastern Democratic Republic of the Congo during 2018–2020. Overall, 25% of patients vaccinated before symptom onset died compared with 63% of unvaccinated patients. Vaccinated patients reported fewer EVD-associated symptoms, had reduced time to clearance of viral load, and had reduced length of stay at the Ebola Treatment Center. After controlling for confounders, vaccination was strongly associated with decreased deaths. Reduction in deaths was not affected by timing of vaccination before or after EVD exposure. These findings support use of preexposure and postexposure recombinant vesicular stomatitis virus–Zaire Ebola virus vaccine as an intervention associated with improved death rates, illness, and recovery time among patients with EVD.     

Evaluation of novel HIV vaccine candidates using recombinant vesicular stomatitis virus vector produced in serum-free Vero cell cultures

Acquired Immune Deficiency Syndrome (AIDS) in humans is a result of the destruction of the immune system caused by Human Immunodeficiency Virus (HIV) infection. This serious epidemic is still progressing world-wide. Despite advances in treatment, a safe and effective preventive HIV vaccine is desired to combat this disease, and to save millions of lives. However, such a vaccine is not available yet although extensive amounts of resources in research and development have been invested over three decades. In light of the recently approved Ebola virus disease vaccine based on a recombinant vesicular stomatitis virus (rVSV-ZEBOV), we present the results of our work on three novel VSV-vectored HIV vaccine candidates. We describe the design, rescue, production and purification method and evaluate their immunogenicity in mice prior to preclinical studies that will be performed in non-human primates. The production of each of the three candidate vaccines (rVSV-B6-NL4.3Env/SIVtm, rVSV-B6-NL4.3Env/Ebtm and rVSV-B6-A74Env(PN6)/SIVtm) was evaluated in small scale in Vero cells and it was found that production kinetics on Vero cells vary depending on the HIV gp surface protein used. Purified virus preparations complied with the WHO restrictions for the residual DNA and host cell protein contents. Finally, when administered to mice, all three rVSV-HIV vaccine candidates induced an HIV gp140-specific antibody response.     

Establishing herd immunity against Ebola through vaccination

ObjectivesIn response to recent concern regarding Ebola outbreaks, this study aims to (1) determine the relationship between vaccination coverage and herd immunity, (2) determine the vaccination coverage necessary to establish herd immunity for previous Ebola viruses, and (3) recommend vaccination coverage thresholds for future Ebola viruses.MethodsHerd immunity thresholds needed to block transmission of Ebola virus were determined using vaccine efficacy and number of secondary cases per infected case during an entire infectious period.ResultsIn past Ebola outbreaks 42.2–63.0% of the population would need to be vaccinated in order to prevent transmission and outbreaks. Assuming 80% vaccine efficacy as reported by phase I clinical trials, 52.7–78.7% of the population would require vaccination coverage in order to establish herd immunity. In recent ring vaccination trials which considered the vaccine to be 100% effective after 10 days, 42.2–63.0% of the population would need to be vaccinated.ConclusionFor future Ebola outbreaks, the spread of the virus can be prevented by vaccinating certain percentages of the population depending on vaccine efficacy and number of secondary cases per infected case.     

The use of pseudotypes to study viruses,virus sero-epidemiology and vaccination

The globalization of the world's economies, accompanied by increasing international travel, changing climates, altered human behaviour and demographics is leading to the emergence of different viral diseases, many of which are highly pathogenic and hence are considered of great public and animal health importance. To undertake basic research and therapeutic development, many of these viruses require handling by highly trained staff in BSL-3/4 facilities not readily available to the majority of the global R&D community. In order to circumvent the enhanced biosafety requirement, the development of non-pathogenic, replication-defective pseudotyped viruses is an effective and established solution to permit the study of many aspects of virus biology in a low containment biosafety level (BSL)-1/2 laboratory. Under the spectre of the unfolding Ebola crisis, this timely conference (the second to be organised by the Viral Pseudotype Unit, www.viralpseudotypeunit.info*) discusses the recent advances in pseudotype technology and how it is revolutionizing the study of important human and animal pathogens (human and avian influenza viruses, rabies/lyssaviruses, HIV, Marburg and Ebola viruses). Key topics addressed in this conference include the exploitation of pseudotypes for serology and serosurveillance, immunogenicity testing of current and next-generation vaccines and new pseudotype assay formats (multiplexing, kit development).*The first pseudotype-focused Euroscicon conference organised by the Viral Pseudotype Unit was recently reviewed [1].     

Vaccines against Ebola virus

We have just witnessed the largest and most devastating outbreak of Ebola virus disease, which highlighted the urgent need for development of an efficacious vaccine that could be used to curtail future outbreaks. Prior to 2014, there had been limited impetus worldwide to develop a vaccine since the virus was first discovered in 1976. Though too many lives were lost during this outbreak, it resulted in the significantly accelerated clinical development of a number of candidate vaccines through an extraordinary collaborative global effort coordinated by the World Health Organisation (WHO) and involving a number of companies, trial centres, funders, global stakeholders and agencies. We have acquired substantial safety and immunogenicity data on a number of vaccines in Caucasian and African populations. The rapid pace of events led to the initiation of the landmark efficacy trial testing the rVSV-vectored vaccine, which showed high level efficacy in an outbreak setting when deployed using an innovative ring vaccination strategy. Though the Public Health Emergency of International Concern (PHEIC) declared by the WHO has now been lifted, the global scientific community faces numerous challenges ahead to ensure that there is a licensed, deployable vaccine available for use in future outbreaks for at least the Zaire and Sudan strains of Ebola virus. There remain several unanswered questions on the durability of protection, mechanistic immunological correlates and preferred deployment strategies. This review outlines a brief history of the development of Ebola vaccines, the significant progress made since the scale of the outbreak became apparent, some lessons learnt and how they could shape future development of vaccines and the management of similar outbreaks.     

The effect of gamma-irradiation conditions on the immunogenicity of whole-inactivated Influenza A virus vaccine

Gamma-irradiation, particularly an irradiation dose of 50 kGy, has been utilised widely to sterilise highly pathogenic agents such as Ebola, Marburg Virus, and Avian Influenza H5N1. We have reported previously that intranasal vaccination with a gamma-irradiated Influenza A virus vaccine (γ-Flu) results in cross-protective immunity. Considering the possible inclusion of highly pathogenic Influenza strains in future clinical development of γ-Flu, an irradiation dose of 50 kGy may be used to enhance vaccine safety beyond the internationally accepted Sterility Assurance Level (SAL). Thus, we investigated the effect of irradiation conditions, including high irradiation doses, on the immunogenicity of γ-Flu. Our data confirm that irradiation at low temperatures (using dry-ice) is associated with reduced damage to viral structure compared with irradiation at room temperature. In addition, a single intranasal vaccination with γ-Flu irradiated on dry-ice with either 25 or 50 kGy induced seroconversion and provided complete protection against lethal Influenza A challenge. Considering that low temperature is expected to reduce the protein damage associated with exposure to high irradiation doses, we titrated the vaccine dose to verify the efficacy of 50 kGy γ-Flu. Our data demonstrate that exposure to 50 kGy on dry-ice is associated with limited effect on vaccine immunogenicity, apparent only when using very low vaccine doses. Overall, our data highlight the immunogenicity of influenza virus irradiated at 50 kGy for induction of high titre antibody and cytotoxic T-cell responses. This suggests these conditions are suitable for development of γ-Flu vaccines based on highly pathogenic Influenza A viruses.     

Setting-up an Ebola vaccine trial in a remote area of the Democratic Republic of the Congo: Challenges,mitigations, and lessons learned

Since the largest Ebola outbreak in West Africa (2013–2016) highlighted the potential threat of the Ebola virus to the world, several vaccines have been under development by different pharmaceutical companies. To obtain vaccine licensure, vaccine trials assessing the safety, immunogenicity and efficacy of new vaccines among different populations (e.g. different in age, gender, race, and ethnicity) play a crucial role. However, while this deadly disease mainly affects Central and West Africa, clinical trial regulations are becoming increasingly complex and consequently more expensive, influencing the affected low- and middle-income countries (LMICs) in performing high quality clinical trials. Consequently, the completion of such trials in LMICs takes more time and vaccines and drugs take longer to be licensed. To overcome some of the obstacles faced, the EBOVAC3 consortium, funded by the European Union’s Innovative Medicines Initiative and the Coalition for Epidemic Preparedness Innovations, enabled high quality vaccine trials in Central and West Africa through extensive North-South collaborations. In this article, the encountered challenges, mitigations, recommendations and lessons learned from setting-up an Ebola vaccine trial in a remote area of the Democratic Republic of Congo are presented. These challenges are grouped into eight categories: (1) Regulatory, political and ethical, (2) Trial documents, (3) International collaborations, (4) Local trial staff, (5) Community engagement and sensitization, (6) Logistics, (7) Remoteness and climate conditions, (8) Financial. By sharing the encountered challenges, implemented mitigations and lessons learned for each of these categories, we hope to prepare and inform other researchers aspiring a well-functioning clinical trial unit in similar remote settings in LMICs. ClinicalTrials.gov identifier: NCT04186000.     

Progress towards a vaccine against Ebola to meet emergency medical countermeasure needs

The Ebola virus epidemic in West Africa proved to be the largest in the history of filovirus outbreaks, causing the World Health Organization to declare a public health emergency of international concern in August of 2014. In collaboration with domestic and international partners, the Biomedical Advanced Research and Development Authority (BARDA) initiated several vaccine development projects in support of the overall response efforts. The urgency associated with the epidemic triggered the clinical evaluation of lead vaccine candidates starting in late 2014. Here we will discuss development of the lead vaccine candidates for Ebola virus, specifically Zaire ebolavirus.