A comprehensive insight on the challenges for COVID-19 vaccine: A lesson learnt from other viral vaccines

The aim of this study is to comprehensively analyze previous viral vaccine programs and identify potential challenges and effective measures for the COVID-19 vaccine program. Previous viral vaccine programs, such as those for HIV, Zika, Influenza, Ebola, Dengue, SARS, and MERS, were evaluated. Paramount challenges were identified, including quasi-species, cross-reactivity, duration of immunity, revaccination, mutation, immunosenescence, and adverse events related to viral vaccines. Although a large population has been vaccinated, mutations in SARS-CoV-2 and adverse events related to vaccines pose significant challenges. Previous vaccine programs have taught us that predicting the final outcome of the current vaccine program for COVID-19 cannot be determined at a given state. Long-term follow-up studies are essential. Validated preclinical studies, long-term follow-up studies, alternative therapeutic approaches, and alternative vaccines are necessary.

Effects of adjuvants in a rabies-vectored Ebola virus vaccine on protection from surrogate challenge

Ebola virus is the primary contributor to the global threat of filovirus severe hemorrhagic fever, and Ebola virus disease has a case fatality rate of 50-90%. An inactivated, bivalent filovirus/rabies virus vaccine, FILORAB1, consists of recombinant rabies virus virions expressing the Ebola virus glycoprotein. FILORAB1 is immunogenic and protective from Ebola virus challenge in mice and non-human primates, and protection is enhanced when formulated with toll-like receptor 4 agonist Glucopyranosyl lipid adjuvant (GLA) in a squalene oil-in-water emulsion (SE). Through an adjuvant comparison in mice, we demonstrate that GLA-SE improves FILORAB1 efficacy by activating the innate immune system and shaping a Th1-biased adaptive immune response. GLA-SE adjuvanted mice and those adjuvanted with the SE component are better protected from surrogate challenge, while Th2 alum adjuvanted mice are not. Additionally, the immune response to FILORAB1 is long-lasting, as exhibited by highly-maintained serum antibody titers and long-lived cells in the spleen and bone marrow.

Lyophilized Filovirus Glycoprotein Vaccines: Peroxides in a Vaccine Formulation with Polysorbate 80-Containing Adjuvant are Associated with Reduced Neutralizing Antibody Titers in Both Mice and Non-Human Primates

Zaire ebolavirus, Sudan ebolavirus, and Marburg marburgvirus are the filoviruses most commonly associated with human disease. Previously, we administered a three-dose regimen of trivalent vaccines comprising glycoprotein antigens from each virus in mice and non-human primates (NHPs). The vaccines, which contained a polysorbate 80-stabilized squalane-in-water emulsion adjuvant and were lyophilized from a solution containing trehalose, produced high antibody levels against all three filovirus antigens. Subsequently, single-vial formulations containing a higher concentration of adjuvant were generated for testing in NHPs, but these vaccines elicited lower neutralizing antibody titers in NHPs than previously tested formulations. In order to explain these results, in the current work we measured the size of adjuvant emulsion droplets and the peroxide levels present in the vaccines after lyophilization and reconstitution and tested the effects of these variables on the immune response in mice. Increases in squalane droplet sizes were observed when the ratio of adjuvant to trehalose was increased beyond a critical value, but antibody and neutralizing antibody titers in mice were independent of the droplet size. Higher levels of peroxides in the vaccines correlated with higher concentrations of adjuvant in the formulations, and higher peroxide levels were associated with increased levels of oxidative damage to glycoprotein antigens. Neutralizing titers in mice were inversely correlated with peroxide levels in the vaccines, but peroxide levels could be reduced by adding free methionine, resulting in retention of high neutralizing antibody titers. Overall, the results suggest that oxidation of glycoprotein antigens by peroxides in the polysorbate 80-stabilized squalane-in-water emulsion adjuvant, but not lyophilization-induced increases in adjuvant emulsion droplet size may have been responsible for the decreased neutralizing titers seen in formulations containing higher amounts of adjuvant.

Multimerization of Ebola GPΔmucin on protein nanoparticle vaccines has minimal effect on elicitation of neutralizing antibodies

Ebola virus (EBOV), a member of the Filoviridae family of viruses and a causative agent of Ebola Virus Disease (EVD), is a highly pathogenic virus that has caused over twenty outbreaks in Central and West Africa since its formal discovery in 1976. The only FDA-licensed vaccine against Ebola virus, rVSV-ZEBOV-GP (Ervebo®), is efficacious against infection following just one dose. However, since this vaccine contains a replicating virus, it requires ultra-low temperature storage which imparts considerable logistical challenges for distribution and access. Additional vaccine candidates could provide expanded protection to mitigate current and future outbreaks. Here, we designed and characterized two multimeric protein nanoparticle subunit vaccines displaying 8 or 20 copies of GPΔmucin, a truncated form of the EBOV surface protein GP. Single-dose immunization of mice with GPΔmucin nanoparticles revealed that neutralizing antibody levels were roughly equivalent to those observed in mice immunized with non-multimerized GPΔmucin trimers. These results suggest that some protein subunit antigens do not elicit enhanced antibody responses when displayed on multivalent scaffolds and can inform next-generation design of stable Ebola virus vaccine candidates.

Developing a Stabilizing Formulation of a Live Chimeric Dengue Virus Vaccine Dry Coated on a High-Density Microarray Patch

Alternative delivery systems such as the high-density microarray patch (HD-MAP) are being widely explored due to the variety of benefits they offer over traditional vaccine delivery methods. As vaccines are dry coated onto the HD-MAP, there is a need to ensure the stability of the vaccine in a solid state upon dry down. Other challenges faced are the structural stability during storage as a dried vaccine and during reconstitution upon application into the skin. Using a novel live chimeric virus vaccine candidate, BinJ/DENV2-prME, we explored a panel of pharmaceutical excipients to mitigate vaccine loss during the drying and storage process. This screening identified human serum albumin (HSA) as the lead stabilizing excipient. When bDENV2-coated HD-MAPs were stored at 4 °C for a month, we found complete retention of vaccine potency as assessed by the generation of potent virus-neutralizing antibody responses in mice. We also demonstrated that HD-MAP wear time did not influence vaccine deposition into the skin or the corresponding immunological outcomes. The final candidate formulation with HSA maintained ~100% percentage recovery after 6 months of storage at 4 °C.

Single-vial filovirus glycoprotein vaccines: Biophysical characteristics and immunogenicity after co-lyophilization with adjuvant

Zaire ebolavirus (EBOV), Sudan ebolavirus (SUDV), and Marburg marburgvirus (MARV) are the most prevalent and pathogenic species of filovirus. Previously, we showed that glycoprotein antigens from each virus could be lyophilized to create thermostable monovalent subunit vaccines. However, cross-protection is not expected from the monovalent vaccines and therefore developing a trivalent filovirus vaccine would be desirable. Subunit protein vaccines often require the addition of an adjuvant to sufficiently boost the immunogenicity. Typically, liquid suspensions or emulsions of adjuvants and lyophilized antigens are stored in separate vials to avoid destabilizing interactions and are only mixed immediately before administration. Herein, we describe the development and characterization of monovalent and trivalent filovirus vaccines that are co-lyophilized with a squalane-in-water emulsion adjuvant. We found that the single-vial presentation retained adjuvant particle diameter and zeta potential after lyophilization and reconstitution. Furthermore, the trivalent vaccines elicited high antibody levels against all three antigens in mice and non-human primates. These results advance the prospect of developing a single-vial trivalent filovirus vaccine, which would enable easier distribution and administration of the vaccine to resource-poor areas.

Recombinant Protein Filovirus Vaccines Protect Cynomolgus Macaques From Ebola, Sudan, and Marburg Viruses

Ebola (EBOV), Marburg (MARV) and Sudan (SUDV) viruses are the three filoviruses which have caused the most fatalities in humans. Transmission from animals into the human population typically causes outbreaks of limited scale in endemic regions. In contrast, the 2013-16 outbreak in several West African countries claimed more than 11,000 lives revealing the true epidemic potential of filoviruses. This is further emphasized by the difficulty seen with controlling the 2018-2020 outbreak of EBOV in the Democratic Republic of Congo (DRC), despite the availability of two emergency use-approved vaccines and several experimental therapeutics targeting EBOV. Moreover, there are currently no vaccine options to protect against the other epidemic filoviruses. Protection of a monovalent EBOV vaccine against other filoviruses has never been demonstrated in primate challenge studies substantiating a significant void in capability should a MARV or SUDV outbreak of similar magnitude occur. Herein we show progress on developing vaccines based on recombinant filovirus glycoproteins (GP) from EBOV, MARV and SUDV produced using the Drosophila S2 platform. The highly purified recombinant subunit vaccines formulated with CoVaccine HT™ adjuvant have not caused any safety concerns (no adverse reactions or clinical chemistry abnormalities) in preclinical testing. Candidate formulations elicit potent immune responses in mice, guinea pigs and non-human primates (NHPs) and consistently produce high antigen-specific IgG titers. Three doses of an EBOV candidate vaccine elicit full protection against lethal EBOV infection in the cynomolgus challenge model while one of four animals infected after only two doses showed delayed onset of Ebola Virus Disease (EVD) and eventually succumbed to infection while the other three animals survived challenge. The monovalent MARV or SUDV vaccine candidates completely protected cynomolgus macaques from infection with lethal doses of MARV or SUDV. It was further demonstrated that combinations of MARV or SUDV with the EBOV vaccine can be formulated yielding bivalent vaccines retaining full efficacy. The recombinant subunit vaccine platform should therefore allow the development of a safe and efficacious multivalent vaccine candidate for protection against Ebola, Marburg and Sudan Virus Disease.

Preservation of Quaternary Structure in Thermostable, Lyophilized Filovirus Glycoprotein Vaccines: A Search for Stability-Indicating Assays

The filoviruses Zaire ebolavirus (EBOV), Marburg marburgvirus (MARV), and Sudan ebolavirus (SUDV) are some of the most lethal infectious agents known. To date, the Zaire ebolavirus vaccine (ERVEBO®) is the only United States Food and Drug Administration (FDA) approved vaccine available for any species of filovirus. However, the ERVEBO® vaccine requires cold-chain storage not to exceed -60 °C. Such cold-chain requirements are difficult to maintain in low- and middle-income countries where filovirus outbreaks originate. To improve the thermostability of filovirus vaccines in order to potentially relax or eliminate these cold-chain requirements, monovalent subunit vaccines consisting of glycoproteins from EBOV, MARV, and SUDV were stabilized within amorphous disaccharide glasses through lyophilization. Lyophilized formulations and liquid controls were incubated for up to 12 weeks at 50 °C to accelerate degradation. To identify a stability-indicating assay appropriate for monitoring protein degradation and immunogenicity loss during these accelerated stability studies, filovirus glycoprotein secondary, tertiary, and quaternary structures and vaccine immunogenicity were measured. Size-exclusion chromatography was the most sensitive indicator of glycoprotein stability in the various formulations for all three filovirus immunogens. Degradation of the test vaccines during accelerated stability studies was reflected in changes in quaternary structure, which were discernible with size-exclusion chromatography. Filovirus glycoproteins in glassy lyophilized formulations retained secondary, tertiary, and quaternary protein structure over the incubation period, whereas the proteins within liquid controls both aggregated to form higher molecular weight species and dissociated from their native quaternary structure to form a variety of structurally-perturbed lower molecular weight species.

Examination of the effect of agitation on the potency of the Ebola Zaire vaccine rVSVΔG-ZEBOV-GP

The Ebolavirus vaccine (rVSVΔG-ZEBOV-GP) is stored at -80 to -60 °C and should be kept frozen for transport. Due to significant logistical challenges, frozen transport is not feasible for some remote locations. To determine if local distribution at 2-8 °C is a potential option for these locations, a study was conducted to evaluate the impact of agitation on the thawed vaccine. After up to 7 days of constant agitation, no impact on vaccine potency was evident for the agitated vaccine versus the corresponding vaccine kept stationary at 2-8 °C. In conclusion, in-country transport of the Ebolavirus vaccine, rVSVΔG-ZEBOV-GP, at 2-8 °C appears to be a feasible option for those remote locations where significant logistical challenges prohibit transporting the vaccine at -80 to -60 °C.

Safety, immunogenicity and risk-benefit analysis of rVSV-ΔG-ZEBOV-GP (V920) Ebola vaccine in Phase I-III clinical trials across regions

To evaluate the risk-benefits balance of the rVSV-ΔG-ZEBOV-GP vaccine. We performed a systematic review to summarize data on safety, immunogenicity and efficacy. About 17,600 adults and 234 children received 11 different doses of the V920 vaccine ranging from 3000 to 100 million and 20 million plaque-forming units, respectively, during Phase I-III clinical trials. Cases of severe but transient arthritis were reported in about six and 0.08% of vaccinees in high-income countries (HICs) and low-middle-income countries (LMICs), respectively. The 20 million plaque-forming units dose yielded GP-specific antibody titres which peaked at day 28 with a pooled geometric mean titres of 2557.7 (95% CI: 1665.5-3934.2) versus 1156.9 (95% CI: 832.5-1649.2) but with similar seroconversion rates at 96% (95% CI: 87-100) versus 100% (95% CI: 90-100) for HICs and LMICs, respectively. Data from stringent Phase I-II clinical trials in LMICs and HICs and from the ring efficacy trials yielded a good risk-benefit balance of the V920 vaccine in adults, but also in children and pregnant and lactating women and HIV-infected people.

Inactivated Rabies Virus-Based Ebola Vaccine Preserved by Vaporization Is Heat-Stable and Immunogenic Against Ebola and Protects Against Rabies Challenge

BACKGROUND

Ebola virus (EBOV) is a highly lethal member of the Filoviridae family associated with human hemorrhagic disease. Despite being a sporadic disease, it caused a large outbreak in 2014-2016 in West Africa and another outbreak recently in the Democratic Republic of Congo. Several vaccine candidates are currently in preclinical and clinical studies but none are stable without cold chain storage.

METHODS

We used preservation by vaporization (PBV), a novel processing technology to heat-stabilize FiloRab1 (inactivated rabies-based Ebola vaccine), a candidate Ebola vaccine, and stored the vials at temperatures ranging from 4°C to 50°C for 10 days to 12 months. We immunized Syrian hamsters with the best long-term stable FiloRab1 PBV vaccines and challenged them with rabies virus (RABV).

RESULTS

Syrian hamsters immunized with FiloRab1 PBV-processed vaccines stored at temperatures of 4°C and 37°C for 6 months, and at 50°C for 2 weeks, seroconverted against both RABV-G and EBOV-GP. Notably, all of the FiloRab1 PBV vaccines proved to be 100% effective in a RABV challenge model.

CONCLUSIONS

We successfully demonstrated that the FiloRab1 PBV vaccines are stable and efficacious for up to 6 months when stored at temperatures ranging from 4°C to 37°C and for up to 2 weeks at 50°C.

Recombinant vesicular stomatitis virus vector vaccines for WHO blueprint priority pathogens

The devastating Ebola virus (EBOV) outbreak in West Africa in 2013-2016 has flagged the need for the timely development of vaccines for high-threat pathogens. To be better prepared for new epidemics, the WHO has compiled a list of priority pathogens that are likely to cause future outbreaks and for which R&D efforts are, therefore, paramount (R&D Blueprint: https://www.who.int/blueprint/priority-diseases/en/ ). To this end, the detailed characterization of vaccine platforms is needed. The vesicular stomatitis virus (VSV) has been established as a robust vaccine vector backbone for infectious diseases for well over a decade. The recent clinical trials testing the vaccine candidate VSV-EBOV against EBOV disease now have added a substantial amount of clinical data and suggest VSV to be an ideal vaccine vector candidate for outbreak pathogens. In this review, we discuss insights gained from the clinical VSV-EBOV vaccine trials as well as from animal studies investigating vaccine candidates for Blueprint pathogens.

Intradermal SynCon® Ebola GP DNA Vaccine Is Temperature Stable and Safely Demonstrates Cellular and Humoral Immunogenicity Advantages in Healthy Volunteers

Background

Nonlive vaccine approaches that are simple to deliver and stable at room temperature or 2–8°C could be advantageous in controlling future Ebola virus (EBOV) outbreaks. Using an immunopotent DNA vaccine that generates protection from lethal EBOV challenge in small animals and nonhuman primates, we performed a clinical study to evaluate both intramuscular (IM) and novel intradermal (ID) DNA delivery.

Methods

Two DNA vaccine candidates (INO-4201 and INO-4202) targeting the EBOV glycoprotein (GP) were evaluated for safety, tolerability, and immunogenicity in a phase 1 clinical trial. The candidates were evaluated alone, together, or in combination with plasmid-encoded human cytokine interleukin-12 followed by in vivo electroporation using either the CELLECTRA® IM or ID delivery devices.

Results

The safety profile of all 5 regimens was shown to be benign, with the ID route being better tolerated. Antibodies to EBOV GP were generated by all 5 regimens with the fastest and steepest rise observed in the ID group. Cellular immune responses were generated with every regimen.

Conclusions

ID delivery of INO-4201 was well tolerated and resulted in 100% seroreactivity after 2 doses and elicited interferon-γ T-cell responses in over 70% of subjects, providing a new approach for EBOV prevention in diverse populations.

Clinical Trials Registration. NCT02464670.

Baited vaccines: A strategy to mitigate rodent-borne viral zoonoses in humans

Rodents serve as the natural reservoir and vector for a variety of pathogens, some of which are responsible for severe and life-threatening disease in humans. Despite the significant impact in humans many of these viruses, including Old and New World hantaviruses as well as Arenaviruses, most have no specific vaccine or therapeutic to treat or prevent human infection. The recent success of wildlife vaccines to mitigate rabies in animal populations offers interesting insight into the use of similar strategies for other zoonotic agents of human disease. In this review, we discuss the notion of using baited vaccines as a means to interrupt the transmission of viral pathogens between rodent reservoirs and to susceptible human hosts.

Chimpanzee adenoviral vectors as vaccines for outbreak pathogens

The 2014-15 Ebola outbreak in West Africa highlighted the potential for large disease outbreaks caused by emerging pathogens and has generated considerable focus on preparedness for future epidemics. Here we discuss drivers, strategies and practical considerations for developing vaccines against outbreak pathogens. Chimpanzee adenoviral (ChAd) vectors have been developed as vaccine candidates for multiple infectious diseases and prostate cancer. ChAd vectors are safe and induce antigen-specific cellular and humoral immunity in all age groups, as well as circumventing the problem of pre-existing immunity encountered with human Ad vectors. For these reasons, such viral vectors provide an attractive platform for stockpiling vaccines for emergency deployment in response to a threatened outbreak of an emerging pathogen. Work is already underway to develop vaccines against a number of other outbreak pathogens and we will also review progress on these approaches here, particularly for Lassa fever, Nipah and MERS.

Ebola outbreak preparedness planning: a qualitative study of clinicians' experiences

Objectives

The 2014–15 Ebola outbreak in West Africa highlighted the challenges many hospitals face when preparing for the potential emergence of highly contagious diseases. This study examined the experiences of frontline health care professionals in an Australian hospital during the outbreak, with a focus on participant views on information, training and preparedness, to inform future outbreak preparedness planning.

Study design

Semi-structured interviews were conducted with 21 healthcare professionals involved in Ebola preparedness planning, at a hospital in Australia.

Methods

The data were systematically coded to discover key themes in participants' accounts of Ebola preparedness.

Results

Three key themes identified were: 1) the impact of high volumes of—often inconsistent—information, which shaped participants' trust in authority; 2) barriers to engagement in training, including the perceived relative risk Ebola presented; and finally, 3) practical and environmental impediments to preparedness.

Conclusions

These clinicians' accounts of Ebola preparedness reveal a range of important factors which may influence the relative success of outbreak preparedness and provide guidance for future responses. In particular, they illustrate the critical importance of clear communication and guidelines for staff engagement with, and implementation of training. An important outcome of this study was how individual assessments of risk and trust are produced via, and overlap with, the dynamics of communication, training and environmental logistics. Consideration of the dynamic ways in which these issues intersect is crucial for fostering an environment that is suitable for managing an infectious threat such as Ebola.

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Outbreak communication needs to be rigorously controlled for consistency and transparency at all levels.

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Risk perception is influenced by lack of trust in the communication provided.

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Assessment of training effectiveness and feasibility for outbreak threats should include frontline clinicians.

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Dynamics of communication and mistrust can strongly influence the ability of an organisation to implement best practice.

An Inactivated Rabies Virus-Based Ebola Vaccine, FILORAB1, Adjuvanted With Glucopyranosyl Lipid A in Stable Emulsion Confers Complete Protection in Nonhuman Primate Challenge Models

The 2013-2016 West African Ebola virus (EBOV) disease outbreak was the largest filovirus outbreak to date. Over 28 000 suspected, probable, or confirmed cases have been reported, with a 53% case-fatality rate. The magnitude and international impact of this EBOV outbreak has highlighted the urgent need for a safe and efficient EBOV vaccine. To this end, we demonstrate the immunogenicity and protective efficacy of FILORAB1, a recombinant, bivalent, inactivated rabies virus-based EBOV vaccine, in rhesus and cynomolgus monkeys. Our results demonstrate that the use of the synthetic Toll-like receptor 4 agonist glucopyranosyl lipid A in stable emulsion (GLA-SE) as an adjuvant increased the efficacy of FILORAB1 to 100% protection against lethal EBOV challenge, with no to mild clinical signs of disease. Furthermore, all vaccinated subjects developed protective anti-rabies virus antibody titers. Taken together, these results support further development of FILORAB1/GLA-SE as an effective preexposure EBOV vaccine.

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.