Implementation of an Ebola virus disease vaccine clinical trial during the Ebola epidemic in Liberia: Design, procedures, and challenges

Perceptions, attitudes, and willingness of healthcare and frontline workers to participate in an Ebola vaccine trial in Uganda

BACKGROUND

Understanding the knowledge, perception and attitudes towards Ebola vaccines is an important factor in ensuring future use of these vaccines. A qualitative methods study embedded in an Ebola vaccine immunogenicity and safety trial (NCT04028349) was conducted to explore the knowledge and perceptions of healthcare (HCWs) and frontline workers (FLWs), about Ebola vaccines and their willingness to participate or recommend participation in Uganda.

METHOD

We carried out focus group discussions and semi-structured interviews before and after vaccination, with 70 HCWs and FLWs who consented to participate in the trial, and in the qualitative component, from August to September 2019. Data were analysed using thematic content analysis.

RESULTS

Respondents showed good knowledge about Ebola and the vaccines in general, and had wide access to information through several channels, including the study team. On prevention, particular attention was given to effective communication within health facilities. Misconceptions were mainly around route of transmission, animal origin and types of vaccines. Previous fears were based on rumours circulating in the community, mainly about the presence of the virus in the vaccine, side effects and intention to harm (e.g. by "the whites"), ultimately insisting on transparency, trust and involvement of local leaders. Acceptability of participation was motivated by the need to protect self and others, and the willingness to advance research. Majority were willing to recommend participation to their community.

CONCLUSIONS

Overall, information sharing leads to a better understanding and acceptance of vaccine trials and a positive vaccination experience can be a deciding factor in the acceptance of others. Particular attention should be paid to involving the community in addressing misconceptions and fears, while ensuring that participants have access to vaccination sites in terms of transport, and that they are properly accommodated at the study site including staying for a reasonable period of time.

Research ethics and public trust in vaccines: the case of COVID-19 challenge trials

Despite their clearly demonstrated safety and effectiveness, approved vaccines against COVID-19 are commonly mistrusted. Nations should find and implement effective ways to boost vaccine confidence. But the implications for ethical vaccine development are less straightforward than some have assumed. Opponents of COVID-19 vaccine challenge trials, in particular, made speculative or empirically implausible warnings on this matter, some of which, if applied consistently, would have ruled out most COVID-19 vaccine trials and many non-pharmaceutical responses.

Translational success of fundamental virology: a VSV-vectored Ebola vaccine

Ebola virus disease (EVD) caused by Ebola virus (EBOV) is a severe, often fatal, hemorrhagic disease. A critical component of the public health response to curb EVD epidemics is the use of a replication-competent, recombinant vesicular stomatitis virus (rVSV)-vectored Ebola vaccine, rVSVΔG-ZEBOV-GP (ERVEBO). In this Gem, we will discuss the past and ongoing development of rVSVΔG-ZEBOV-GP, highlighting the importance of basic science and the strength of public-private partnerships to translate fundamental virology into a licensed VSV-vectored Ebola vaccine.

Best practices and lessons learned from implementing a massive Ebola vaccination program: Summarizing UMURINZI team experience

Background and Aims

The unified Rwandan initiative for national ZEBOVAC immunization (UMURINZI) program's community engagement component was enacted to mobilize and vaccinate high-risk community members. This article describes best practices and lessons learned from the implementation of UMURINZI, a large-scale Ebola vaccination program.

Methods

The population deemed to be at risk for EVD consisted of people who frequently cross Rwanda and the Democratic Republic of Congo (DRC) borders including those coming from Kigali City, potential first responders who have not previously been vaccinated against EVD, as well as people who reside in high-risk border-proximate areas of the Rubavu and Rusizi districts in the Western Province of Rwanda. These districts were selected because of their proximity to high-traffic borders linking Rwanda to DRC's cities near an active Ebola outbreak. Volunteers of this program were adults, adolescents, and children aged 2 years or above who resided in the selected communities. Recruitment at the sites was conducted in close collaboration with each health area's Community Health Workers (CHWs). Volunteers were informed that the program involved being fully vaccinated (two doses of Ebola vaccines) within 2 months apart in the allocated vaccination sites.

Results

Lessons learned were categorized into four pillars: infrastructure, leadership, myths, and partnership with respect. The best practices that were used during the implementation of the UMURINZI program were the results of a collaboration among CHWs, the involvement of national and local leaders, the use of a comprehensive engagement plan, and training. The study also had limitations.

Conclusion

We described best practices and lessons learned during the implementation of the UMURINZI program in Rwanda. These practices and lessons learned represent promising options that could contribute to better community members' participation in mass vaccination programs. Hence, we demonstrated that rigorously designed community awareness and sensitization programs are effective for the implementation of similar programs in resource-limited settings.

Ebola vaccine uptake and attitudes among healthcare workers in North Kivu, Democratic Republic of the Congo, 2021

Introduction

During the 2018-2020 Ebola virus disease (EVD) outbreak in the eastern part of the Democratic Republic of the Congo (DRC), prevention and control measures, such as Ebola vaccination were challenging by community mistrust. We aimed to understand perceptions regarding Ebola vaccination and identify determinants of Ebola vaccine uptake among HCWs.

Methods

In March 2021, we conducted a cross-sectional survey among 438 HCWs from 100 randomly selected health facilities in three health zones (Butembo, Beni, Mabalako) affected by the 10th EVD outbreak in North Kivu, DRC. HCWs were eligible if they were ≥ 18 years and were working in a health facility during the outbreak. We used survey logistic regression to assess correlates of first-offer uptake (i.e., having received the vaccine the first time it was offered vs. after subsequent offers).

Results

Of the 438 HCWs enrolled in the study, 420 (95.8%) reported that they were eligible and offered an Ebola vaccine. Among those offered vaccination, self-reported uptake of the Ebola vaccine was 99.0% (95% confidence interval (CI) [98.5-99.4]), but first-offer uptake was 70.2% (95% CI [67.1, 73.5]). Nearly all HCWs (94.3%; 95% CI [92.7-95.5]) perceived themselves to be at risk of contracting EVD. The most common concern was that the vaccine would cause side effects (65.7%; 95% CI [61.4-69.7]). In the multivariable analysis, mistrust of the vaccine source or how the vaccine was produced decreased the odds of first-time uptake.

Discussion

Overall uptake of the Ebola vaccine was high among HCWs, but uptake at the first offer was substantially lower, which was associated with mistrust of the vaccine source. Future Ebola vaccination efforts should plan to make repeated vaccination offers to HCWs and address their underlying mistrust in the vaccines, which can, in turn, improve community uptake.

CDC's COVID-19 International Vaccine Implementation and Evaluation Program and Lessons from Earlier Vaccine Introductions

The US Centers for Disease Control and Prevention (CDC) supports international partners in introducing vaccines, including those against SARS-CoV-2 virus. CDC contributes to the development of global technical tools, guidance, and policy for COVID-19 vaccination and has established its COVID-19 International Vaccine Implementation and Evaluation (CIVIE) program. CIVIE supports ministries of health and their partner organizations in developing or strengthening their national capacities for the planning, implementation, and evaluation of COVID-19 vaccination programs. CIVIE's 7 priority areas for country-specific technical assistance are vaccine policy development, program planning, vaccine confidence and demand, data management and use, workforce development, vaccine safety, and evaluation. We discuss CDC's work on global COVID-19 vaccine implementation, including priorities, challenges, opportunities, and applicable lessons learned from prior experiences with Ebola, influenza, and meningococcal serogroup A conjugate vaccine introductions.

Quantifying Efficiency Gains of Innovative Designs of Two-Arm Vaccine Trials for COVID-19 Using an Epidemic Simulation Model

Clinical trials of a vaccine during an epidemic face particular challenges, such as the pressure to identify an effective vaccine quickly to control the epidemic, and the effect that time-space-varying infection incidence has on the power of a trial. We illustrate how the operating characteristics of different trial design elements maybe evaluated using a network epidemic and trial simulation model, based on COVID-19 and individually randomized two-arm trials with a binary outcome. We show that "ring" recruitment strategies, prioritizing participants at an imminent risk of infection, can result in substantial improvement in terms of power in the model we present. In addition, we introduce a novel method to make more efficient use of the data from the earliest cases of infection observed in the trial, whose infection may have been too early to be vaccine-preventable. Finally, we compare several methods of response-adaptive randomization (RAR), discussing their advantages and disadvantages in the context of our model and identifying particular adaptation strategies that preserve power and estimation properties, while slightly reducing the number of infections, given an effective vaccine.

Challenges of evaluating and modelling vaccination in emerging infectious diseases

Outbreaks of emerging pathogens pose unique methodological and practical challenges for the design, implementation, and evaluation of vaccine efficacy trials. Lessons learned from COVID-19 highlight the need for innovative and flexible study design and application to quickly identify promising candidate vaccines. Trial design strategies should be tailored to the dynamics of the specific pathogen, location of the outbreak, and vaccine prototypes, within the regional socioeconomic constraints. Mathematical and statistical models can assist investigators in designing infectious disease clinical trials. We introduce key challenges for planning, evaluating, and modelling vaccine efficacy trials for emerging pathogens.

Africa's preparedness towards COVID-19 vaccines: Demand and acceptability challenges

To date, the response to coronavirus disease (COVID-19) in many African countries has been quick, forward-looking and adjustable in spite of the continent's limited resources. These responses were triggered by the continuous increase in cases and deaths, which have necessitated speedy development of an effective vaccine. It is anticipated that African governments and public health officials will show more transparency, and provide evidence-based strategies to support COVID-19 vaccines and design equitable as well as effective vaccine delivery plans for the populace. To this end, this review analysed Africa's preparedness and response towards COVID-19 vaccines, potential demand, acceptability and distribution challenges related to the management of the virus. The review takes stock of context-specific vaccine preparedness; the demand for vaccine and associated challenges; as well as vaccine accessibility and its distribution. The review offers insightful approaches and strategies by which African countries can maximize benefits from the COVID-19 vaccines to overcome the virus. These include the pursuance of vaccines that may help confer immunity or protection against the virus in the light of contextual circumstances of specific African countries, including sociocultural and economic issues among other factors.

How can community engagement in health research be strengthened for infectious disease outbreaks in Sub-Saharan Africa? A scoping review of the literature

BACKGROUND

Community engagement (CE) is a well-established practical and scholarly field, recognised as core to the science and ethics of health research, for which researchers and practitioners have increasingly asked questions about desired standards and evaluation. In infectious disease outbreak contexts, questions may be more complex. However, it is unclear what body of knowledge has been developed for CE specifically as it applies to emerging infectious diseases. This scoping review seeks to describe (1) How CE has been conceptualised and understood; and (2) What conclusions have research teams reached on the effectiveness of CE in these settings, including challenges and facilitators.

METHODS

We used a scoping review framework by Arksey and O'Malley (Int J Soc Res Methodol 8:19-32, 2005) to structure our review. We conducted a brainstorming session and initial trial search to inform the protocol, search terms, and strategy. Three researchers discussed, developed and applied agreed screening tools and selection criteria to the final search results. Five researchers used the screening tools to screen abstracts and full text for inclusion by consensus. Additional publications were sought from references of retrieved publications and an expert call for literature. We analysed and reported emerging themes qualitatively.

RESULTS

We included 59 papers from a total of 722 articles derived from our trial and final literature searches, as well as a process of "citation chasing" and an expert call for grey literature. The core material related exclusively to health research trials during the 2014-2016 West Africa Ebola outbreak. We synthesized reports on components of effectiveness of CE to identify and propose three themes as essential elements of effective CE.

CONCLUSIONS

While there is a large volume of literature documenting CE activities in infectious disease research settings generally, there are few accounts of effectiveness dimensions of CE. Our review proposes three themes to facilitate the effectiveness of CE initiatives as essential elements of CE activities in infectious diseases studies: (1) Communication towards building collaborative relationships; (2) Producing contextual knowledge; and (3) Learning lessons over time. As there were relatively few in-depth accounts of CE from our literature review, documentation and accounts of CE used in health research should be prioritised.

A Descriptive-Multivariate Analysis of Community Knowledge, Confidence, and Trust in COVID-19 Clinical Trials among Healthcare Workers in Uganda

Background—misinformation and mistrust often undermines community vaccine uptake, yet information in rural communities, especially of developing countries, is scarce. This study aimed to identify major challenges associated with coronavirus disease 2019 (COVID-19) vaccine clinical trials among healthcare workers and staff in Uganda. Methods—a rapid exploratory survey was conducted over 5 weeks among 260 respondents (66% male) from healthcare centers across the country using an online questionnaire. Twenty-seven questions assessed knowledge, confidence, and trust scores on COVID-19 vaccine clinical trials from participants in 46 districts in Uganda. Results—we found low levels of knowledge (i.e., confusing COVID-19 with Ebola) with males being more informed than females (OR = 1.5, 95% CI: 0.7–3.0), and mistrust associated with policy decisions to promote herbal treatments in Uganda and the rushed international clinical trials, highlighting challenges for the upcoming Oxford–AstraZeneca vaccinations. Knowledge, confidence and trust scores were higher among the least educated (certificate vs. bachelor degree holders). We also found a high level of skepticism and possible community resistance to DNA recombinant vaccines, such as the Oxford–AstraZeneca vaccine. Preference for herbal treatments (38/260; 14.6%, 95% CI: 10.7–19.3) currently being promoted by the Ugandan government raises major policy concerns. High fear and mistrust for COVID-19 vaccine clinical trials was more common among wealthier participants and more affluent regions of the country. Conclusion—our study found that knowledge, confidence, and trust in COVID-19 vaccines was low among healthcare workers in Uganda, especially those with higher wealth and educational status. There is a need to increase transparency and inclusive participation to address these issues before new trials of COVID-19 vaccines are initiated.

Adult and paediatric haematology and clinical chemistry laboratory reference limits for Liberia

Background

As more research is conducted in Liberia, there is a need for laboratory reference limits for common chemistry and haematology values based on a healthy population. Reference limits from the United States may not be applicable.

Objective

The aim of this study was to present laboratory reference ranges from a Liberian population and compare them to United States ranges.

Methods

Serum chemistry and haematology values from 2529 adults and 694 children and adolescents obtained from two studies conducted in Liberia between 2015 to 2017 were used to determine reference limits. After removing outliers, the reference limits defined by the 2.5th and 97.5th percentiles were determined by sex in three age groups (6–11, 12–17, and 18+ years).

Results

The median (interquartile range) of adults was 29 (23, 37) years; 44% were female. The median (interquartile range) for children and adolescents was 12 (9, 15) years; 53% were female. Several reference ranges determined using Liberian participants differed from those in the US. For chemistries, a high percentage of both adults and children/adolescents had high serum chloride levels based on United States ranges. For haematology, a high percentage of Liberian participants had haemoglobin and related assays below the lower limit of United States ranges.

Conclusion

Chemistry and haematology reference intervals determined for a Liberian population of healthy individuals should be considered for establishing eligibility criteria and monitoring of laboratory adverse events for clinical trials as well as for use in clinical settings in Liberia and perhaps for other countries in Western Africa.

Immune correlates analysis using vaccinees from test negative designs

Determining the effect of vaccine-induced immune response on disease risk is an important goal of vaccinology. Typically, immune correlates analyses are conducted prospectively with immune response measured shortly after vaccination and subsequent disease status regressed on immune response. In outbreaks and rare disease settings, collecting samples from all vaccinees is not feasible. The test negative design is a retrospective design used to measure vaccine efficacy where symptomatic individuals who present at a clinic are assessed for relevant disease (cases) or some other disease (controls) and vaccination status ascertained. This article proposes that test negative vaccinees have immune response to vaccine assessed both for relevant (e.g., Ebola) and irrelevant (e.g., vector) proteins. If the latter immune response is unaffected by active (Ebola) infection, and is correlated with the relevant immune response, it can serve as a proxy for the immune response of interest proximal to infection. We show that logistic regression using imputed immune response as the covariate and case disease as outcome can estimate the prospective immune response slope and detail the assumptions needed for unbiased inference. The method is evaluated by simulation under various scenarios including constant and decaying immune response. A simulated dataset motivated by ring vaccination for an ongoing Ebola outbreak is analyzed.

Medical research during the COVID-19 pandemic

The current pandemic of coronavirus disease 2019 (COVID-19) which was first detected in Wuhan, China in December 2019 is caused by the novel coronavirus named severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). The virus has quickly spread to a large number of countries leading to a great number of deaths. Unfortunately, till today there is no specific treatment or vaccination for SARS-CoV-2. Most of the suggested treatment medications are based on in vitro laboratory investigations, experimental animal models, or previous clinical experience in treating similar viruses such as SARS-CoV-1 or other retroviral infections. The running of any clinical trial during a pandemic is affected at multiple levels. Reasons for this include patient hesitancy or inability to continue investigative treatments due to self-isolation/quarantine, or limited access to public places (including hospitals). Additional barriers relate to health care professionals being committed to other critical tasks or quarantining themselves due to contact with COVID-19 positive patients. The best research approaches are those that adapt to such external unplanned obstacles. Ongoing clinical trials before COVID-19 pandemic have the potential for identifying important therapies in the long-term if they can be completed as planned. However, these clinical trials may require modifications due a pandemic such as this one to ensure the rights, safety, and wellbeing of participants as well as medical staff involved in the conduction of clinical trials. Clinical trials initiated during the pandemic must be time-efficient and flexible due to high contagiousness of severe acute respiratory syndrome coronavirus 2, the significant number of reported deaths, and time constraints needed to perform high quality clinical trials, enrolling adequate sample sizes. Collaboration between different countries as well as implementation of innovative clinical trial designs are essential to successfully complete such initiatives during the current pandemic. Studies looking at the long term sequalae of COVID-19 are also of importance as recent publications describe multi-organ involvement. Long term follow-up of COVID-19 survivors is thus also important to identify possible physical and mental health sequellae.

Serostatus cutoff levels and fold increase to define seroresponse to recombinant vesicular stomatitis virus - Zaire Ebola virus envelope glycoprotein vaccine: An evidence-based analysis

The recombinant vesicular stomatitis virus - Zaire Ebola virus envelope glycoprotein (rVSVΔG-ZEBOV-GP) vaccine is a live recombinant vesicular stomatitis virus (VSV) where the VSV G protein is replaced with ZEBOV-GP. To better understand the immune response after receiving the rVSVΔG-ZEBOV-GP vaccine, the current analyses evaluated different definitions of seroresponse that differentiate vaccine and placebo recipients enrolled in a placebo-controlled clinical trial (PREVAIL; NCT02344407) in which a subset of the study participants had elevated baseline titers. Alternative values for serostatus cutoff (SSCO; 200-500 EU/mL) and/or fold rise (two- to five-fold) were applied to compare their ability to distinguish between participants receiving rVSVΔG-ZEBOV-GP or placebo. The results indicate that an SSCO of 200 EU/mL can be used to define seropositivity at baseline (i.e. pre-vaccination). The use of dual criteria of the same SSCO (200 EU/mL) together with a two-fold rise in antibody level from baseline provided the definition of seroresponse that maximized the statistical significance between vaccine recipients and placebo recipients post-vaccination. Clinical trial registration: NCT02344407.

Logistics of Implementing a Large-scale Typhoid Vaccine Trial in Kathmandu, Nepal

Typhoid fever is estimated to affect over 20 million people per year worldwide, with infants, children, and adolescents in south-central and southeast Asia experiencing the greatest burden of disease. The Typhoid Vaccine Acceleration Consortium (TyVAC) aims to support the introduction of typhoid conjugate vaccines into Gavi-eligible countries in an effort to reduce morbidity and mortality from typhoid. TyVAC-Nepal is a large-scale, participant- and observer-blind, individually randomized, controlled trial evaluating the efficacy of a newly developed typhoid conjugate vaccine in an urban setting in Nepal. In order to effectively deliver the trial, a number of key elements required meticulous planning. Public engagement strategies were considered early, and involved the implementation of a tiered approach. Approximately 300 staff were employed and trained in order to achieve the mass vaccination of 20 000 children aged 9 months to ≤16 years old over a 4-month period. There were 19 vaccination clinics established across the Lalitpur metropolitan city in the Kathmandu valley. Participants will be followed for 2 years post-vaccination to measure the rate reduction of blood culture–confirmed typhoid fever in the vaccination arm as compared to the control arm. The experience of conducting this large-scale vaccine trial suggests that comprehensive planning, continuous monitoring, and an ability to adapt plans in response to feedback are key.

Ebola vaccine? Family first! Evidence from using a brief measure on Ebola vaccine demand in a national household survey during the outbreak in Sierra Leone

BACKGROUND

Vaccination against Ebolavirus is an emerging public health tool during Ebola Virus Disease outbreaks. We examined demand issues related to deployment of Ebolavirus vaccine during the 2014-2015 outbreak in Sierra Leone.

METHODS

A cluster survey was administered to a population-based sample in December 2014 (N = 3540), before any Ebola vaccine was available to the general public in Sierra Leone. Ebola vaccine demand was captured in this survey by three Likert-scale items that were used to develop a composite score and dichotomized into a binary outcome to define high demand. A multilevel logistic regression model was fitted to assess the associations between perceptions of who should be first to receive an Ebola vaccine and the expression of high demand for an Ebola vaccine.

RESULTS

The largest proportion of respondents reported that health workers (35.1%) or their own families (29.5%) should receive the vaccine first if it became available, rather than politicians (13.8%), vaccination teams (9.8%), or people in high risk areas (8.2%). High demand for an Ebola vaccine was expressed by 74.2% of respondents nationally. The odds of expressing high demand were 13 times greater among those who said they or their families should be the first to take the vaccine compared to those who said politicians should be the first recipients (adjusted odds ratio [aOR] 13.0 [95% confidence interval [CI] 7.8-21.6]). The ultra-brief measure of the Ebola vaccine demand demonstrated acceptable scale reliability (Cronbach's α = 0.79) and construct validity (single-factor loadings > 0.50).

CONCLUSION

Perceptions of who should be the first to get the vaccine was associated with high demand for Ebola vaccine around the peak of the outbreak in Sierra Leone. Using an ultra-brief measure of Ebola vaccine demand is a feasible solution in outbreak settings and can help inform development of future rapid assessment tools.

Developing Vaccines for SARS-CoV-2 and Future Epidemics and Pandemics: Applying Lessons from Past Outbreaks

The COVID-19 pandemic is a stark reminder of the heavy toll that emerging infectious diseases (EIDs) with epidemic and pandemic potential can inflict. Vaccine development, scale-up, and commercialization is a long, expensive, and risky enterprise that requires substantial upfront planning and offers no guarantee of success. EIDs are a particularly challenging target for global health preparedness, including for vaccine development. Insufficient attention has been given to challenges, lessons learned, and potential solutions to support and sustain vaccine industry engagement in vaccine development for EIDs. Drawing from lessons from the most recent Ebola epidemic in the Democratic Republic of the Congo, as well as the 2009 H1N1 influenza, 2014-2016 Ebola, and 2015-16 Zika outbreaks preceding it, we offer our perspective on challenges facing EID vaccine development and recommend additional solutions to prioritize in the near term. The 6 recommendations focus on reducing vaccine development timelines and increasing business certainty to reduce risks for companies. The global health security community has an opportunity to build on the current momentum to design a sustainable model for EID vaccines.

R&D for Emerging Infectious Diseases of Epidemic Potential: Sharing Risks and Benefits Through a New Coalition

The lack of effective vaccines for emerging infectious diseases (EID) of limited market potential, such as Chikungunya and Zika, poses a serious threat to human life and prosperity. Research and development (R&D) for new vaccines for EIDs faces two major challenges. The first is R&D preparedness: that is, to advance EID vaccine candidates to the latest R&D stage possible during non-epidemic times, on the basis of any feasible safety or efficacy data. The second is R&D response: that is, to test the clinical efficacy of vaccine candidates rapidly once an outbreak erupts. To overcome these challenges, the Coalition for Epidemic Preparedness Innovations (CEPI) was established in August 2016. Here, we explore why the realisation of CEPI’s mission—preventing outbreaks of emerging infectious diseases from becoming humanitarian crises—is a global public good, and the crucial role R&D preparedness and R&D response play in providing this good. We next examine why providing this global public good requires incentivising involvement and sharing risks with the private sector. Finally, we explore the potential for CEPI to be an agent mobilising shared responsibilities, including key factors that must be addressed in order for CEPI to demonstrate to governments that collective action is the preferred strategy for preventing future epidemics and strengthening global health security.

The Sierra Leone Trial to Introduce a Vaccine Against Ebola: An Evaluation of rVSV∆G-ZEBOV-GP Vaccine Tolerability and Safety During the West Africa Ebola Outbreak

Clinical Trials Registration

ClinicalTrials.gov [NCT02378753] and Pan African Clinical Trials Registry [PACTR201502001037220].

Participant Retention in a Randomized Clinical Trial in an Outbreak Setting: Lessons From the Sierra Leone Trial to Introduce a Vaccine Against Ebola (STRIVE)

Clinical Trials Registration

ClinicalTrials.gov [NCT02378753] and Pan African Clinical Trials Registry [PACTR201502001037220].

Rapid Establishment of a Cold Chain Capacity of -60°C or Colder for the STRIVE Ebola Vaccine Trial During the Ebola Outbreak in Sierra Leone

Clinical Trials Registration

ClinicalTrials.gov [NCT02378753] and Pan African Clinical Trials Registry [PACTR201502001037220].

Training through malaria research: building capacity in good clinical and laboratory practice in Liberia

Background

Limited health research capacities (HRC) undermine a country’s ability to identify and adequately respond to local health needs. Although numerous interventions to strengthen HRC have been conducted in Africa, there is a need to share the lessons learnt by funding organizations, institutes and researchers. The aim of this report is to identify best practices in HRC strengthening by describing a training programme conducted between 2016 and 2017 at the Saint Joseph’s Catholic Hospital (SJCH) in Monrovia (Liberia).

Methods

A call for trainees was launched at the SJCH, the Liberia Medicines and Health Products Regulatory Authority (LMHRA), the Ministry of Health and Social Welfare, the Mother Pattern College of Health Sciences (MPCHS) and community members. Selected trainees participated in four workshops on Good Clinical Laboratory Practice (GCLP), standard operating procedures (SOP) and scientific communication, as well as in a 5-months eLearning mentoring programme. After the training, a collectively-designed research project on malaria was conducted.

Results

Twenty-one of the 28 trainees (14 from the SJCH, 3 from LMHRA, one from MPCHS, and 10 community representatives) completed the programme satisfactorily. Pre- and post-training questionnaires completed by 9 of the trainees showed a 14% increase in the percentage of correct answers. Trainees participated in a mixed-methods cross-sectional study of Plasmodium falciparum infection among pregnant women at the SJCH. Selected trainees disseminated activities and research outcomes in three international meetings and three scientific publications.

Conclusion

This training-through-research programme successfully involved SJCH staff and community members in a practical research exercise on malaria during pregnancy. The challenge is to ensure that the SJCH remains active in research. Harmonization of effectiveness indicators for HRC initiatives would strengthen the case for investing in such efforts.

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2767-1) contains supplementary material, which is available to authorized users.

Perceptions and acceptability of an experimental Ebola vaccine among health care workers, frontline staff, and the general public during the 2014-2015 Ebola outbreak in Sierra Leone

INTRODUCTION

Experimental Ebola vaccines were introduced during the 2014-2015 Ebola outbreak in West Africa. Planning for the Sierra Leone Trial to Introduce a Vaccine against Ebola (STRIVE) was underway in late 2014. We examined hypothetical acceptability and perceptions of experimental Ebola vaccines among health care workers (HCWs), frontline workers, and the general public to guide ethical communication of risks and benefits of any experimental Ebola vaccine.

METHODS

Between December 2014 and January 2015, we conducted in-depth interviews with public health leaders (N = 31), focus groups with HCWs and frontline workers (N = 20), and focus groups with members of the general public (N = 15) in Western Area Urban, Western Area Rural, Port Loko, Bombali, and Tonkolili districts. Themes were identified using qualitative content analysis.

RESULTS

Across all participant groups, not knowing the immediate and long-term effects of an experimental Ebola vaccine was the most serious concern. Some respondents feared that experimental vaccines may cause Ebola, lead to death, or result in other adverse events. Among HCWs, not knowing the level of protection provided by experimental Ebola vaccines was another concern. HCWs and frontline workers were motivated to help find a vaccine for Ebola to help end the outbreak. General public participants cited positive experiences with routine childhood immunization in Sierra Leone.

DISCUSSION

Our formative assessment prior to STRIVE's implementation in Sierra Leone helped identify concerns, motivations, and information gaps among potential participants of an experimental Ebola vaccine trial, at the time when an unprecedented outbreak was occurring in the country. The findings from this assessment were incorporated early in the process to guide ethical communication of risks and benefits when discussing informed consent for possible participation in the vaccine trial that was launched later in 2015.

Community-informed research on malaria in pregnancy in Monrovia, Liberia: a grounded theory study

BACKGROUND

Liberia is a West African country that needs substantial investment to strengthen its National Malaria Control Programme (NMCP), which was disrupted during the 2014-2016 Ebola epidemic. As elsewhere, Liberian pregnant women are especially vulnerable to malaria. Understanding prevention and treatment-seeking behaviours among the population is crucial to strategize context-specific and women-centred actions, including locally-led malaria research, to improve women's demand, access and use of NMCP strategies against malaria in pregnancy.

METHODS

In 2016, after the Ebola crisis, a qualitative inquiry was conducted in Monrovia to explore populations' insights on the aetiology, prevention and therapeutics of malaria, as well as the community and health workers' perceptions on the utility of malaria research for pregnant women. In-depth interviews and focus group discussions were conducted among pregnant women, traditional community representatives and hospital staff (n = 38), using a feminist interpretation of grounded theory.

RESULTS

The narratives indicate that some Liberians believed in elements other than mosquito bites as causes of malaria; many had a low malaria risk perception and disliked current effective prevention methods, such as insecticide-treated nets; and some would resort to traditional medicine and spiritual care to cure malaria. Access to clinic-based malaria care for pregnant women was reportedly hindered by lack of financial means, by unofficial user fees requested by healthcare workers, and by male partners' preference for traditional medicine. The participants suggested that malaria research in Liberia could help to design evidence-based education to change current malaria prevention, diagnostic and treatment-seeking attitudes, and to develop more acceptable prevention technologies.

CONCLUSION

Poverty, insufficient education on malaria, corruption, and poor trust in healthcare establishment are structural factors that may play a greater role than local traditional beliefs in deterring Liberians from seeking, accessing and using government-endorsed malaria control strategies. To increase access to and uptake of preventive and biomedical care by pregnant women, future malaria research must be informed by people's expressed needs and constructed meanings and values on health, ill health and healthcare.

Unprecedented pace and partnerships: the story of and lessons learned from one Ebola vaccine program

INTRODUCTION

The Ebola epidemic in West Africa from 2014 to 2016 was unique in its size, location, and duration; this article reviews the experiences and lessons learned for one vaccine candidate developed during the outbreak and discusses critical gaps that still exist today which will need to be addressed for successful end to end emerging infectious disease vaccine product development in the future.

AREAS COVERED

Through the formation of numerous international partnerships, the rVSVΔG-ZEBOV-GP vaccine advanced through Phase I/II/III clinical trials which resulted in favorable Phase III efficacy results. Key lessons learned that could be used to facilitate future vaccine development efforts include sufficient preclinical work in relevant animal models, innovative partnerships created to pool resources and expertise, and 'hyper' coordination and communication among partners to build trust and ensure an adequate regulatory package needed to license a vaccine.

EXPERT COMMENTARY

As evidenced by the 2014-2016 outbreak in West Africa as well as the two other most recent outbreaks in the Democratic Republic of the Congo in 2018, there is an urgent need to develop new models for emerging infection vaccine development where trusted partners come together and where the development of vaccines is a shared responsibility conducted in advance of the next crisis.

Reliably picking the best endpoint

Endpoint selection in clinical trials involves a variety of considerations. One important consideration is the sample size required to power a future clinical trial. In this work, we define the sample size ratio, θ, as the ratio of sample sizes required to power a future trial. We consider in detail the setting of continuous endpoints where a Welch's t-statistic is used to analyze the data. We develop an estimator that depends on the squared ratio of estimated standardized treatment effects, and the quadrant on the plane in which they fall. We evaluate bootstrap and profile likelihood methods for construction of confidence intervals. Generalizations to other endpoints and testing of nonnested models are discussed. The methods are applied to analyze two different assays that measure antibody abundance using data from an Ebola vaccine field trial.

Choices in vaccine trial design in epidemics of emerging infections

In a Policy Forum, Marc Lipsitch and colleagues discuss trial design issues in infectious disease outbreaks.

Use of the Filovirus Animal Non-Clinical Group (FANG) Ebola virus immuno-assay requires fewer study participants to power a study than the Alpha Diagnostic International assay

As part of the scientific community's development of medical countermeasures against Ebola virus disease, optimization of standardized assays for product evaluation is paramount. The recent outbreak heightened awareness to the scarcity of available assays and limited information on performance and reproducibility. To evaluate the immunogenicity of vaccines entering Phase I-III trials and to identify survivors, two enzyme-linked immunosorbent assays, the Filovirus Animal Non-Clinical Group assay and the Alpha Diagnostics International assay, were evaluated for detection of immunoglobulin G against Ebola virus glycoprotein. We found that the Filovirus Animal Nonclinical Group assay produced a wider range of relative antibody concentrations, higher assay precision, larger relative accuracy range, and lower regional background. Additionally, to sufficiently power a vaccine trial, use of the Filovirus Animal Nonclinical Group assay would require one third the number of participants than the Alpha Diagnostics International assay. This reduction in needed study participants will require less money, fewer man hours, and much less time to evaluate vaccine immunogenicity.

'Researchers have love for life': opportunities and barriers to engage pregnant women in malaria research in post-Ebola Liberia

BACKGROUND

Adoption of prevention and therapeutic innovations to ensure that National Malaria Control Programmes meet their incidence reduction targets is highly dependent on the conduct of rigorous clinical trials. In Liberia, malaria control virtually halted during the recent Ebola epidemic, and could enormously benefit from innovations to protect its most vulnerable populations, including pregnant women, against malaria. Health policy-planners could feel more inclined to adopt novel interventions with demonstrated safety and efficacy when trialled among their women population. However, pregnant women are especially vulnerable when targeted as research participants. Whilst some studies in the region attempted to understand the ethical issues around the conduct of clinical research, there is need of such information from Liberia to inform future malaria research.

METHODS

This is a grounded theory study that aims to understand the barriers and opportunities for pregnant women to consent to participate in malaria research in Liberia. The study was conducted between November 2016 and May 2017 at the St Joseph's Catholic Hospital, Monrovia. In-depth interviews and focus group discussions were held with hospital staff, traditional community representatives, and pregnant women.

RESULTS

According to the participants, useful strategies to motivate pregnant women to consent to participate in malaria research could be providing evidence-based education on malaria and research to the general population and encouraging engagement of traditional leaders in research design and community mobilization. Fears and suspicions towards research and researchers, which were amplified during the conduct of Ebola vaccine and drug clinical trials, may influence women's acceptance and willingness to engage in malaria research. Population's mistrust in the public healthcare system might hinder their acceptance of research, undermining the probability of their benefiting from any improved malaria control intervention.

CONCLUSION

Benchmarking for acceptable practices from previous public health interventions; building community discussion and dissemination platforms; and mapping communication and information errors from how previous research interventions were explained to the Liberian population, are strategies that might help ensure a safe and fully informed participation of pregnant women in malaria research. Inequity issues impeding access and use of biomedical care for women must be tackled urgently.

From bench to almost bedside: the long road to a licensed Ebola virus vaccine

INTRODUCTION

The Ebola virus (EBOV) disease epidemic during 2014-16 in West Africa has accelerated the clinical development of several vaccine candidates that have demonstrated efficacy in the gold standard nonhuman primate (NHP) model, namely cynomolgus macaques.

AREAS COVERED

This review discusses the pre-clinical research and if available, clinical evaluation of the currently available EBOV vaccine candidates, while emphasizing the translatability of pre-clinical data generated in the NHP model to clinical data in humans.

EXPERT OPINION

Despite the existence of many successful EBOV vaccine candidates in the pre-clinical stages, only two platforms became the focus of Phase 2/3 efficacy trials in Liberia, Sierra Leone, and Guinea near the peak of the epidemic: the Vesicular stomatitis virus (VSV)-vectored vaccine and the chimpanzee adenovirus type 3 (ChAd3)-vectored vaccine. The results of three distinct clinical trials involving these candidates may soon pave the way for a licensed, safe and efficacious EBOV vaccine to help combat future epidemics.

Phase 2 Placebo-Controlled Trial of Two Vaccines to Prevent Ebola in Liberia

BACKGROUND

The safety and efficacy of vaccines to prevent Ebola virus disease (EVD) were unknown when the incidence of EVD was peaking in Liberia.

METHODS

We initiated a randomized, placebo-controlled, phase 3 trial of the chimpanzee adenovirus 3 vaccine (ChAd3-EBO-Z) and the recombinant vesicular stomatitis virus vaccine (rVSV∆G-ZEBOV-GP) in Liberia. A phase 2 subtrial was embedded to evaluate safety and immunogenicity. Because the incidence of EVD declined in Liberia, the phase 2 component was expanded and the phase 3 component was eliminated.

RESULTS

A total of 1500 adults underwent randomization and were followed for 12 months. The median age of the participants was 30 years; 36.6% of the participants were women. During the week after the administration of vaccine or placebo, adverse events occurred significantly more often with the active vaccines than with placebo; these events included injection-site reactions (in 28.5% of the patients in the ChAd3-EBO-Z group and 30.9% of those in the rVSV∆G-ZEBOV-GP group, as compared with 6.8% of those in the placebo group), headache (in 25.1% and 31.9%, vs. 16.9%), muscle pain (in 22.3% and 26.9%, vs. 13.3%), feverishness (in 23.9% and 30.5%, vs. 9.0%), and fatigue (in 14.0% and 15.4%, vs. 8.8%) (P<0.001 for all comparisons); these differences were not seen at 1 month. Serious adverse events within 12 months after injection were seen in 40 participants (8.0%) in the ChAd3-EBO-Z group, in 47 (9.4%) in the rVSV∆G-ZEBOV-GP group, and in 59 (11.8%) in the placebo group. By 1 month, an antibody response developed in 70.8% of the participants in the ChAd3-EBO-Z group and in 83.7% of those in the rVSV∆G-ZEBOV-GP group, as compared with 2.8% of those in the placebo group (P<0.001 for both comparisons). At 12 months, antibody responses in participants in the ChAd3-EBO-Z group (63.5%) and in those in the rVSV∆G-ZEBOV-GP group (79.5%) remained significantly greater than in those in the placebo group (6.8%, P<0.001 for both comparisons).

CONCLUSIONS

A randomized, placebo-controlled phase 2 trial of two vaccines that was rapidly initiated and completed in Liberia showed the capability of conducting rigorous research during an outbreak. By 1 month after vaccination, the vaccines had elicited immune responses that were largely maintained through 12 months. (Funded by the National Institutes of Allergy and Infectious Diseases and the Liberian Ministry of Health; PREVAIL I ClinicalTrials.gov number, NCT02344407 .).

Six-Month Safety Data of Recombinant Vesicular Stomatitis Virus-Zaire Ebola Virus Envelope Glycoprotein Vaccine in a Phase 3 Double-Blind, Placebo-Controlled Randomized Study in Healthy Adults

Background

This study (NCT02503202) evaluated the safety of recombinant vesicular stomatitis virus-Zaire Ebola virus envelope glycoprotein vaccine (rVSVΔG-ZEBOV-GP).

Methods

Overall, 1197 subjects were randomized 2:2:2:2:1; 1194 were vaccinated with 1 dose of 1 of 3 lots of rVSVΔG- ZEBOV-GP (2 × 107 plaque-forming units [pfu], n = 797; combined-lots group), a single high-dose lot of rVSVΔG-ZEBOV-GP (1 × 108 pfu, n = 264; high-dose group), or placebo (n = 133). Daily temperatures and adverse events (AEs) were recorded days 1 to 42 postvaccination. Solicited AEs included injection-site AEs from days 1 to 5, and joint pain, joint swelling, vesicular lesions (blisters), and rashes from days 1 to 42. Serious AEs (SAEs) were recorded through 6 months postvaccination.

Results

Fever (≥38.0°C) was observed in 20.2% of combined lots (3.2% with ≥39.0°C), 32.2% of high-dose (4.3% with ≥39.0°C), and 0.8% of placebo (0.8% with ≥39.0°C). Incidences of AEs of interest (days 1-42) were arthralgia (17.1% combined lots, 20.4% high-dose, 3.0% placebo), arthritis (5.1% combined lots, 4.2% high-dose, 0.0% placebo), and rash (3.8% combined lots, 3.8% high-dose, 1.5% placebo). Twenty-one SAEs and 2 deaths were reported, all assessed by investigators as unrelated to vaccine.

Conclusions

rVSVΔG-ZEBOV-GP was generally well-tolerated, with increased rates of injection-site and systemic AEs compared to placebo, and no vaccine-related SAEs or deaths. These findings support the use of rVSVΔG-ZEBOV-GP vaccine in persons at risk for Ebola virus disease.

Clinical Trials Registration

NCT02503202.

Conventional Wisdom versus Actual Outcomes: Challenges in the Conduct of an Ebola Vaccine Trial in Liberia during the International Public Health Emergency

Clinical trials are challenging endeavors. Planning and implementing an investigational vaccine trial in Liberia, in the midst of an Ebola virus disease (EVD) epidemic that World Health Organization classified a public health emergency of international concern, presented extraordinary challenges. Normally, years of preparation and a litany of tasks lay the groundwork for a successful, randomized, blinded, placebo-controlled trial focused on safety and efficacy. Difficult research settings, unpredictable events, and other unique circumstances can add complexity. The setting in Liberia was especially problematic due to an infrastructure still badly damaged following a lengthy civil war and a very fragile health-care system that was further devastated by the EVD outbreak. The Partnership for Research on Vaccines in Liberia I EVD vaccine trial was planned and implemented in less than 3 months by a Liberian and U.S. research partnership, and its Phase II substudy was fully enrolled 3 months later. Contrasting conventional wisdom with trial outcomes offers an opportunity to compare early assumptions, barriers encountered, and adaptive strategies used, with end results. Understanding what was learned can inform future trial responses when disease outbreaks, especially in resource-poor locations with minimal infrastructure, pose a significant threat to public health.

Establishment of a research pharmacy to support Ebola clinical research in Liberia

OBJECTIVE

This article describes the establishment of a research pharmacy to support the Partnership for Research on Ebola Vaccines in Liberia (PREVAIL) vaccine study for Ebola virus disease.

SETTING

This article describes the establishment of the pharmacy element to support the overall research program during an Ebola outbreak in Monrovia, Liberia, in 2014 and 2015.

PRACTICE INNOVATION

The need for the rapid establishment of infrastructure to support the Liberia-United States joint clinical research partnership in response to the emerging Ebola virus disease provided the opportunity for collaboration among Liberian and U.S. pharmacists.

PRACTICE DESCRIPTION

Resource austere and research naïve.

EVALUATION

Research pharmacy prepared and randomized 1500 vaccinations in support of PREVAIL.

RESULTS

Experiences of the Liberian and U.S. pharmacists involved in the program are described.

CONCLUSION

The partnership was successful in the conduct of the study. More importantly, the capacity for Liberian pharmacists to support clinical research was established. In addition, the U.S. team learned several important lessons that will help prepare them for responding to research needs in future infectious disease outbreaks.

Using simulation to aid trial design: Ring-vaccination trials

BACKGROUND

The 2014-6 West African Ebola epidemic highlights the need for rigorous, rapid clinical trial methods for vaccines. A challenge for trial design is making sample size calculations based on incidence within the trial, total vaccine effect, and intracluster correlation, when these parameters are uncertain in the presence of indirect effects of vaccination.

METHODS AND FINDINGS

We present a stochastic, compartmental model for a ring vaccination trial. After identification of an index case, a ring of contacts is recruited and either vaccinated immediately or after 21 days. The primary outcome of the trial is total vaccine effect, counting cases only from a pre-specified window in which the immediate arm is assumed to be fully protected and the delayed arm is not protected. Simulation results are used to calculate necessary sample size and estimated vaccine effect. Under baseline assumptions about vaccine properties, monthly incidence in unvaccinated rings and trial design, a standard sample-size calculation neglecting dynamic effects estimated that 7,100 participants would be needed to achieve 80% power to detect a difference in attack rate between arms, while incorporating dynamic considerations in the model increased the estimate to 8,900. This approach replaces assumptions about parameters at the ring level with assumptions about disease dynamics and vaccine characteristics at the individual level, so within this framework we were able to describe the sensitivity of the trial power and estimated effect to various parameters. We found that both of these quantities are sensitive to properties of the vaccine, to setting-specific parameters over which investigators have little control, and to parameters that are determined by the study design.

CONCLUSIONS

Incorporating simulation into the trial design process can improve robustness of sample size calculations. For this specific trial design, vaccine effectiveness depends on properties of the ring vaccination design and on the measurement window, as well as the epidemiologic setting.

A Perspective on the Development of Plant-Made Vaccines in the Fight against Ebola Virus

The Ebola virus (EBOV) epidemic indicated a great need for prophylactic and therapeutic strategies. The use of plants for the production of biopharmaceuticals is a concept being adopted by the pharmaceutical industry, with an enzyme for human use currently commercialized since 2012 and some plant-based vaccines close to being commercialized. Although plant-based antibodies against EBOV are under clinical evaluation, the development of plant-based vaccines against EBOV essentially remains an unexplored area. The current technologies for the production of plant-based vaccines include stable nuclear expression, transient expression mediated by viral vectors, and chloroplast expression. Specific perspectives on how these technologies can be applied for developing anti-EBOV vaccines are provided, including possibilities for the design of immunogens as well as the potential of the distinct expression modalities to produce the most relevant EBOV antigens in plants considering yields, posttranslational modifications, production time, and downstream processing.

Assessment and Optimization of the GeneXpert Diagnostic Platform for Detection of Ebola Virus RNA in Seminal Fluid

Recent studies have suggested that Ebola virus (EBOV) ribonucleic acid (RNA) potentially present in the semen of a large number of survivors of Ebola virus disease (EVD) in Western Africa may contribute to sexual transmission of EVD and generate new clusters of cases in regions previously declared EVD-free. These findings drive the immediate need for a reliable, rapid, user-friendly assay for detection of EBOV RNA in semen that is deployable to multiple sites across Western Africa. In this study, we optimized the Xpert EBOV assay for semen samples by adding dithiothreitol. Compared to the assays currently in use in Liberia (including Ebola Zaire Target 1, major groove binder real-time-polymerase chain reaction assays, and original Xpert EBOV assay), the modified Xpert EBOV assay demonstrated greater sensitivity than the comparator assays. Thus, the modified Xpert EBOV assay is optimal for large-scale monitoring of EBOV RNA persistence in male survivors.

[Ethical and health issues posed by the recent Ebola epidemic: What should we learn?]

The recent Ebola epidemic that affected several countries in Africa, with very high mortality and a pandemic threat, posed problems of justice, public health, prevention, treatment and research, each of which has relevant ethical issues. Despite severe initial difficulties, an effective international response was achieved, whose outcome has left significant teachings to be considered in order to deal with future epidemics or pandemics. In this article, the authors analyze the main problems faced during the Ebola epidemic, including the unequal distribution of health resources between countries, the need for international collaboration, the requirement for a review of the ethical standards of clinical trials in emergencies, and the necessity of an organized global system of prevention and timely response to these outbreaks. Authors conclude that at the present time health is a global issue without borders, that insufficient healthcare resources in some countries poses risks and affects all countries and that the confrontation of the threats of epidemics requires a solution based in universal solidarity. At the same time, a moral duty to investigate should be acknowledged, seeking a balance between sense of urgency, scientific rigor and involvement of local communities.

Pre-Ebola virus disease laboratory system and related challenges in Liberia

Prior to the Ebola virus disease outbreak in Liberia, the laboratory system was duplicative, fragmented and minimally coordinated. The National Reference Laboratory was conceptualised to address the existing challenges by promoting the implementation of effective and sustainable laboratory services in Liberia. However, in a resource-limited environment such as Liberia, progress regarding the rebuilding of the health system can be relatively slow, while efforts to sustain the transient gains remain a key challenge for the Ministry of Health. In this paper, we describe the pre-Ebola virus disease laboratory system in Liberia and its prevailing efforts to address future emerging infectious diseases, as well as current Infectious diseases, all of which are exacerbated by poverty. We conclude that laboratory and diagnostic services in Liberia have encountered numerous challenges regarding its efforts to strengthen the healthcare delivery system. These challenges include limited trained human resource capacity, inadequate infrastructure, and a lack of coordination. As with most countries in sub-Saharan Africa, when comparing urban and rural settings, diagnostic and clinical services are generally skewed toward urban health facilities and private, faith-based health facilities. We recommend that structured policy be directed at these challenges for national institutions to develop guidelines to improve, strengthen and sustain diagnostic and curative laboratory services to effectively address current infectious diseases and prepare for future emerging and re-emerging infectious diseases.

Ebola vaccines - Where are we?

The 2014-16 Ebola outbreak in West Africa has by far been the largest and most devastating Ebola outbreak so far. At the start of the epidemic only 2 Ebola DNA vaccine candidates had been tested in clinical trials and the correlate of protection in humans was unknown. International stakeholders coordinated by the World Health Organization agreed to fast-track the development of 2 Ebola vaccine candidates, based on adenovirus and vesicular stomatitis virus (VSV) vectors. Phase I and II clinical trials were initiated in the autumn of 2014 and found both vaccines to be acceptable for proceeding to phase III trials. Despite the epidemic waning in the spring of 2015, by July 2015 preliminary results from a phase III trial in Guinea proved the Ebola VSV vaccine to be effective.

Toward an Effective Ebola Virus Vaccine

Long-term control of viral outbreaks requires the use of vaccines to impart acquired resistance and ensuing protection. In the wake of an epidemic, established immunity against a particular disease can limit spread and significantly decrease mortality. Creation of a safe and efficacious vaccine against Ebola virus (EBOV) has proven elusive so far, but various inventive strategies are now being employed to counteract the threat of outbreaks caused by EBOV and related filoviruses. Here, we present a current overview of progress in the field of Ebola virus vaccine development.

Simian adenoviruses as vaccine vectors

Replication incompetent human adenovirus serotype 5 (HAdV-C5) has been extensively used as a delivery vehicle for gene therapy proteins and infectious disease antigens. These vectors infect replicating and nonreplicating cells, have a broad tissue tropism, elicit high immune responses and are easily purified to high titers. However, the utility of HAdV-C5 vectors as potential vaccines is limited due to pre-existing immunity within the human population that significantly reduces the immunogenicity of HAdV-C5 vaccines. In recent years, adenovirus vaccine development has focused on simian-derived adenoviral vectors, which have the desirable vector characteristics of HAdV-C5 but with negligible seroprevalence in the human population. Here, we discuss recent advances in simian adenovirus vaccine vector development and evaluate current research specifically focusing on clinical trial data.