In Silico Structure-Based Vaccine Design.

Structure-based vaccine design (SBVD) is an important technique in computational vaccine design that uses structural information on a targeted protein to design novel vaccine candidates. This increasing ability to rapidly model structural information on proteins and antibodies has provided the scientific community with many new vaccine targets and novel opportunities for future vaccine discovery. This chapter provides a comprehensive overview of the status of in silico SBVD and discusses the current challenges and limitations. Key strategies in the field of SBVD are exemplified by a case study on design of COVID-19 vaccines targeting SARS-CoV-2 spike protein.

Ability of SpikoGen®, an Advax-CpG adjuvanted recombinant spike protein vaccine, to induce cross-neutralising antibodies against SARS-CoV-2 variants.

SpikoGen® vaccine is a subunit COVID-19 vaccine expressed in insect cells comprising recombinant spike protein extracellular domain formulated with Advax-CpG55.2™ adjuvant. A Phase 2 trial was conducted in 400 adult participants randomised 3:1 to receive two intramuscular doses of SpikoGen® vaccine or saline placebo 3 weeks apart. Some Phase 2 trial participants later enrolled in a separate booster study and received a third dose of SpikoGen® vaccine. This stored serum was used to assess the ability of SpikoGen® vaccine to induce cross-neutralising antibodies against SARS-CoV-2 variants of concern. Sera taken at baseline and 2 weeks after the second vaccine dose from baseline seronegative Phase 2 subjects was evaluated using a panel of spike pseudotype lentivirus neutralisation assays for the ability to cross-neutralise a wide range of SARS-CoV-2 variants, including Omicron BA.1, BA.2 and BA.4/5. Stored samples of subjects who participated in both the 2-dose Phase 2 trial and a third dose booster trial 6 months later were also analysed for changes in cross-neutralising antibodies over time and dose. Two weeks after the second dose, sera broadly cross-neutralised most variants of concern, albeit with titres against Omicron variants being ~10-fold lower. While Omicron titres fell to low levels 6 months after the second vaccine dose in most subjects, they showed a ~20-fold rise after the third dose booster, after which there was only a ~2-3-fold difference in neutralisation of Omicron and the ancestral strains. Despite being based on the ancestral Wuhan sequence, after two doses, SpikoGen® vaccine induced broadly cross-neutralising serum antibodies. Titres then reduced over time but were rapidly restored by a third dose booster. This resulted in high neutralisation including against the Omicron variants. This data supports ongoing use of SpikoGen® vaccine for protection against recent SARS-CoV-2 Omicron variants.

Disproportionality analysis of adverse neurological and psychiatric reactions with the ChAdOx1 (Oxford-AstraZeneca) and BNT162b2 (Pfizer-BioNTech) COVID-19 vaccines in the United Kingdom.

BACKGROUND: Information on neurological and psychiatric adverse events following immunization (AEFIs) with COVID-19 vaccines is limited. RESEARCH DESIGN & METHODS: We examined and compared neurological and psychiatric AEFIS reports related to BNT162b2 (Pfizer-BioNTech) and ChAdOx1 (Oxford-AstraZeneca) COVID-19 vaccines and recorded in the United Kingdom Medicines and Healthcare products Regulatory Agency between 9 December 2020 and 30 June 2021. RESULTS: As of 30 June 2021, 46.1 million doses of ChAdOx1 and 30.3 million doses of BNT162b2 had been administered. The most frequently reported AEFI was headache with 1,686 and 575 cases per million doses of ChAdOx1 and BNT162b2, respectively. AEFIs more frequently reported after CHAdOx1 compared with BNT162b2 vaccination were Guillain-Barré syndrome (OR, 95% CI = 2.53, 1.82-3.51), freezing (6.66, 3.12-14.22), cluster headache (1.53, 1.28-1.84), migraine (1.23,1.17-1.30), postural dizziness (1.24,1.13-1.37), tremor (2.86, 2.68-3.05), headache (1.40, 1.38-1.43), paresthesia (1.11, 1.06-1.16), delirium (1.85, 1.45-2.36), hallucination (2.20, 1.82-2.66), poor quality sleep (1.53, 1.26-1.85), and nervousness (1.54, 1.26-1.89) Reactions less frequently reported with ChAdOx1 than with BNT162b2 were Bell's palsy (0.47, 0.41-0.55), anosmia (0.58, 0.47-0.71), facial paralysis (0.35, 0.29-0.41), dysgeusia (0.68, 0.62-0.73), presyncope (0.48, 0.42-0.55), syncope (0.63, 0.58-0.67), and anxiety (0.75 (0.67-0.85). CONCLUSION: Neurological and psychiatric AEFIs were relatively infrequent, but each vaccine was associated with a distinctive toxic profile.

We examined reports on adverse neurological and psychiatric effects following immunization with BNT162b2 (Pfizer-BioNTech) and ChAdOx1 (Oxford-AstraZeneca) for COVID-19 to the United Kingdom Medicines and Healthcare products Regulatory Agency between 9 December 2020 and 30 June 2021. Adverse effects following immunization (AEFIs) were relatively infrequent. Compared to BNT162b2, Guillain-Barré syndrome, freezing phenomenon, cluster headache, migraine, postural dizziness, tremor, headache, paresthesia, delirium, hallucination, poor quality sleep, and nervousness were more frequently reported for ChAdOx1. Reactions less frequently reported for ChAdOx1 than for BNT162b2 were Bell's palsy, anosmia, facial paralysis, dysgeusia, presyncope, syncope, and anxiety.

Identifying SARS-CoV-2 Drugs Binding to the Spike Fatty Acid Binding Pocket Using In Silico Docking and Molecular Dynamics.

Drugs against novel targets are needed to treat COVID-19 patients, especially as SARS-CoV-2 is capable of rapid mutation. Structure-based de novo drug design and repurposing of drugs and natural products is a rational approach to discovering potentially effective therapies. These in silico simulations can quickly identify existing drugs with known safety profiles that can be repurposed for COVID-19 treatment. Here, we employ the newly identified spike protein free fatty acid binding pocket structure to identify repurposing candidates as potential SARS-CoV-2 therapies. Using a validated docking and molecular dynamics protocol effective at identifying repurposing candidates inhibiting other SARS-CoV-2 molecular targets, this study provides novel insights into the SARS-CoV-2 spike protein and its potential regulation by endogenous hormones and drugs. Some of the predicted repurposing candidates have already been demonstrated experimentally to inhibit SARS-CoV-2 activity, but most of the candidate drugs have yet to be tested for activity against the virus. We also elucidated a rationale for the effects of steroid and sex hormones and some vitamins on SARS-CoV-2 infection and COVID-19 recovery.

Evaluating the efficacy and safety of SpikoGen®, an Advax-CpG55.2-adjuvanted severe acute respiratory syndrome coronavirus 2 spike protein vaccine: a phase 3 randomized placebo-controlled trial.

OBJECTIVES: We sought to investigate the efficacy and safety of SpikoGen®, a subunit coronavirus disease 2019 (COVID-19) vaccine composed of a recombinant severe acute respiratory syndrome coronavirus 2 spike protein with Advax-CpG55.2™ adjuvant. METHODS: This randomized, placebo-controlled, double-blind, phase 3 trial was conducted on 16 876 participants randomized (3:1) to receive two intramuscular doses of SpikoGen® or a saline placebo 21 days apart. The primary outcome was to assess the efficacy of SpikoGen® in preventing symptomatic COVID-19. Secondary outcomes included safety assessments and evaluation of SpikoGen® vaccine's efficacy in preventing severe COVID-19. The study aimed for 147 COVID-19 symptomatic cases. RESULTS: Overall, 12 657 and 4219 participants were randomized to the SpikoGen® and placebo group and followed for a median of 55 days (interquartile range, 48-60 days) and 51 days (interquartile range, 46-58 days) after 14 days of the second dose, respectively. In the final per-protocol analysis, the number of COVID-19 cases was 247 of 9998 (2.4%) in the SpikoGen® group and 119 of 3069 (3.8%) in the placebo group. This equated to a vaccine efficacy of 43.99% (95% CI, 30.3-55.0%). The efficacy was calculated to be 44.22% (95% CI, 31.13-54.82%) among all participants who received both doses. From 2 weeks after the second dose, 5 of 9998 (0.05%) participants in the SpikoGen® group and 6 of 3069 (0.19%) participants in the placebo group developed severe COVID-19, equating to a vaccine efficacy against severe disease of 77.51% (95% CI, 26.3-93.1%). The SpikoGen® vaccine was well tolerated. DISCUSSION: A 2-dose regimen of SpikoGen® reduced the rate of COVID-19 and severe disease in the wave of the Delta variant.

Mucosal immunization with a delta-inulin adjuvanted recombinant spike vaccine elicits lung-resident immune memory and protects mice against SARS-CoV-2.

Multiple SARS-CoV-2 vaccine candidates have been approved for use and have had a major impact on the COVID-19 pandemic. There remains, however, a significant need for vaccines that are safe, easily transportable and protective against infection, as well as disease. Mucosal vaccination is favored for its ability to induce immune memory at the site of infection, making it appealing for SARS-CoV-2 vaccine strategies. In this study we performed in-depth analysis of the immune responses in mice to a subunit recombinant spike protein vaccine formulated with the delta-inulin adjuvant Advax when administered intratracheally (IT), versus intramuscular delivery (IM). Both routes produced robust neutralizing antibody titers (NAb) and generated sterilizing immunity against SARS-CoV-2. IT delivery, however, produced significantly higher systemic and lung-local NAb that resisted waning up to six months post vaccination, and only IT delivery generated inducible bronchus-associated lymphoid tissue (iBALT), a site of lymphocyte antigen presentation and proliferation. This was coupled with robust and long-lasting lung tissue-resident memory CD4+ and CD8+ T cells that were not observed in IM-vaccinated mice. This study provides a detailed view of the lung-resident cellular response to IT vaccination against SARS-CoV-2 and demonstrates the importance of delivery site selection in the development of vaccine candidates.

Potential COVID-19 Therapies from Computational Repurposing of Drugs and Natural Products against the SARS-CoV-2 Helicase.

Repurposing of existing drugs is a rapid way to find potential new treatments for SARS-CoV-2. Here, we applied a virtual screening approach using Autodock Vina and molecular dynamic simulation in tandem to screen and calculate binding energies of repurposed drugs against the SARS-CoV-2 helicase protein (non-structural protein nsp13). Amongst the top hits from our study were antivirals, antihistamines, and antipsychotics, plus a range of other drugs. Approximately 30% of our top 87 hits had published evidence indicating in vivo or in vitro SARS-CoV-2 activity. Top hits not previously reported to have SARS-CoV-2 activity included the antiviral agents, cabotegravir and RSV-604; the NK1 antagonist, aprepitant; the trypanocidal drug, aminoquinuride; the analgesic, antrafenine; the anticancer intercalator, epirubicin; the antihistamine, fexofenadine; and the anticoagulant, dicoumarol. These hits from our in silico SARS-CoV-2 helicase screen warrant further testing as potential COVID-19 treatments.

Immunogenicity and safety of SpikoGen®, an adjuvanted recombinant SARS-CoV-2 spike protein vaccine as a homologous and heterologous booster vaccination: A randomized placebo-controlled trial.

SpikoGen® is a subunit recombinant spike protein vaccine combined with Advax-CpG55.2™ adjuvant. This COVID-19 vaccine was shown to be safe, immunogenic and efficacious in previous clinical trials. This study aimed to assess the safety and immunogenicity of SpikoGen® vaccine as a homologous and heterologous booster vaccination. This double-blind and randomized placebo-controlled (5:1) trial was performed on 300 already vaccinated participants. SpikoGen® or saline placebo was administered as a booster dose to participants who had received a full two-dose COVID-19 vaccination course. Immunogenicity assessments were done 14 days after the booster dose with the primary immunogenicity outcome seroconversion rate of neutralizing antibodies. Safety outcomes included the incidence of solicited adverse events up to 7 days after the booster dose. SpikoGen® vaccine induced a robust humoral response both as a homologous and heterologous booster, when compared to the placebo. At Day 14, seroconversion of neutralizing antibodies was 76% (95% confidence interval [CI]: 69%-82%) in the SpikoGen® group versus 3% (95% CI: 0%-13%) in the placebo group. The most common local and systemic reported adverse events were injection site pain and fatigue. No serious adverse events were reported. The SpikoGen®-booster induced cross-neutralization of other SARS-CoV-2 variants. Irrespective of the primary vaccine course received, SpikoGen® vaccine showed promising effects as both a homologous and heterologous booster dose. This vaccine also had a good safety profile with no vaccine-associated serious adverse events. On the basis of these results, SpikoGen® vaccine has been approved as a booster dose.

Enhanced Immunogenicity of Inactivated Dengue Vaccines by Novel Polysaccharide-Based Adjuvants in Mice.

Dengue fever, caused by any of four dengue viruses (DENV1-4), is a major global burden. Currently, there is no effective vaccine that prevents infection in dengue naïve populations. We tested the ability of two novel adjuvants (Advax-PEI and Advax-2), using aluminum hydroxide (alum) as control, to enhance the immunogenicity of formalin- or psoralen-inactivated (PIV or PsIV) DENV2 vaccines in mice. Mice were vaccinated on days 0 and 30, and serum samples were collected on days 30, 60, 90, and 101. Neutralizing antibodies were determined by microneutralization (MN) assays, and the geometric mean 50% MN (MN50) titers were calculated. For the PIV groups, after one dose MN50 titers were higher in the novel adjuvant groups compared to the alum control, while MN50 titers were comparable between the adjuvant groups after the second dose. For the PsIV groups, both novel adjuvants induced higher MN50 titers than the alum control after the second dose. Spleen cells were collected on days 45 and 101 for enzyme-linked immunospot (ELISPOT) for IFNγ and IL4. Both PIV and PsIV groups elicited different degrees of IFNγ and IL4 responses. Overall, Advax-2 gave the best responses just ahead of Advax-PEI. Given Advax-2's extensive human experience in other vaccine applications, it will be pursued for further development.

Safety and immunogenicity of SpikoGen®, an Advax-CpG55.2-adjuvanted SARS-CoV-2 spike protein vaccine: a phase 2 randomized placebo-controlled trial in both seropositive and seronegative populations.

OBJECTIVE: We aimed to investigate the immunogenicity and safety of SpikoGen®, a subunit COVID-19 vaccine composed of a recombinant prefusion-stabilized SARS-CoV-2 spike protein combined with the Advax-CpG55.2™ adjuvant, in seronegative and seropositive populations as primary vaccination. METHODS: This randomized, placebo-controlled, double-blind phase 2 trial was conducted on 400 participants randomized 3:1 to receive two doses of 25 µg of SpikoGen® 3 weeks apart or the placebo. The primary safety outcomes were the incidence of solicited adverse events up to 7 days after each dose and unsolicited adverse events up to 28 days after the second dose. The primary immunogenicity outcomes were seroconversion against the S1 protein and the geometric mean concentration of S1 antibodies by days 21 and 35. RESULTS: The SpikoGen® vaccine was well tolerated and no serious adverse events were recorded. The most common solicited adverse events were injection site pain and fatigue, largely graded as mild and transient. By day 35 (2 weeks post second dose), the seroconversion rate against S1 was 63.55 (95% CI: 57.81-69.01) in the SpikoGen® group versus 7.23 (95% CI: 2.7-15.07) in the placebo group. The geometric mean concentration of S1 antibodies was 29.12 (95% CI: 24.32-34.87) in the SpikoGen® group versus 5.53 (95% CI: 4.39-6.97) in the placebo group. Previously infected seropositive volunteers showed a large SARS-CoV-2 humoral response after a single SpikoGen® dose. DISCUSSION: SpikoGen® had an acceptable safety profile and induced promising humoral and cellular immune responses against SARS-CoV-2.

Covax-19/Spikogen® vaccine based on recombinant spike protein extracellular domain with Advax-CpG55.2 adjuvant provides single dose protection against SARS-CoV-2 infection in hamsters.

COVID-19 presents an ongoing global health crisis. Protein-based COVID-19 vaccines that are well-tolerated, safe, highly-protective and convenient to manufacture remain of major interest. We therefore sought to compare the immunogenicity and protective efficacy of a number of recombinant SARS-CoV-2 spike protein candidates expressed in insect cells. By comparison to a full length (FL) spike protein detergent-extracted nanoparticle antigen, the soluble secreted spike protein extracellular domain (ECD) generated higher protein yields per liter of culture and when formulated with either Alum-CpG55.2 or Advax-CpG55.2 combination adjuvants elicited robust antigen-specific humoral and cellular immunity in mice. In hamsters, the spike ECD when formulated with either adjuvant induced high serum neutralizing antibody titers even after a single dose. When challenged with the homologous SARS-CoV-2 virus, hamsters immunized with the adjuvanted spike ECD exhibited reduced viral load in day 1-3 oropharyngeal swabs and day 3 nasal turbinate tissue and had no recoverable infectious virus in day 3 lung tissue. The reduction in lung viral load correlated with less weight loss and lower lung pathology scores. The formulations of spike ECD with Alum-CpG55.2 or Advax-CpG55.2 were protective even after just a single dose, although the 2-dose regimen performed better overall and required only half the total amount of antigen. Pre-challenge serum neutralizing antibody levels showed a strong correlation with lung protection, with a weaker correlation seen with nasal or oropharyngeal protection. This suggests that serum neutralizing antibody levels may correlate more closely with systemic, rather than mucosal, protection. The spike protein ECD with Advax-CpG55.2 formulation (Covax-19® vaccine) was selected for human clinical development.

A Spike Protein-Based Subunit SARS-CoV-2 Vaccine for Pets: Safety, Immunogenicity, and Protective Efficacy in Juvenile Cats.

Whereas, multiple vaccine types have been developed to curb the spread of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) among humans, there are very few vaccines being developed for animals including pets. To combat the threat of human-to-animal, animal-to-animal, and animal-to-human transmission and the generation of new virus variants, we developed a subunit SARS-CoV-2 vaccine which is based on the recombinant spike protein extracellular domain expressed in insect cells and then formulated with appropriate adjuvants. Sixteen 8-12-week-old outbred female and male kittens (n = 4 per group) were randomly assigned into four treatment groups: spike protein alone; spike plus ESSAI oil-in-water (O/W) 1849102 adjuvant; spike plus aluminum hydroxide adjuvant; and a PBS control. All animals were vaccinated intramuscularly twice, 2 weeks apart, with 5 µg of spike protein in a volume of 0.5 ml. On days 0 and 28, serum samples were collected to evaluate anti-spike IgG, antibody inhibition of spike binding to angiotensin-converting enzyme 2 (ACE-2), neutralizing antibodies against wild-type and delta variant viruses, and hematology studies. At day 28, all groups were challenged with SARS-CoV-2 wild-type virus 106 TCID50 intranasally. On day 31, tissue samples (lung, heart, and nasal turbinates) were collected for viral RNA detection, and virus titration. After two immunizations, both vaccines induced high titers of serum anti-spike IgG that inhibited spike ACE-2 binding and neutralized both wild-type and delta variant virus. Both adjuvanted vaccine formulations protected juvenile cats against virus shedding from the upper respiratory tract and viral replication in the lower respiratory tract and hearts. These promising data warrant ongoing evaluation of the vaccine's ability to protect cats against SARS-CoV-2 infection and in particular to prevent transmission.

Computational Repurposing of Drugs and Natural Products Against SARS-CoV-2 Main Protease (Mpro) as Potential COVID-19 Therapies.

We urgently need to identify drugs to treat patients suffering from COVID-19 infection. Drugs rarely act at single molecular targets. Off-target effects are responsible for undesirable side effects and beneficial synergy between targets for specific illnesses. They have provided blockbuster drugs, e.g., Viagra for erectile dysfunction and Minoxidil for male pattern baldness. Existing drugs, those in clinical trials, and approved natural products constitute a rich resource of therapeutic agents that can be quickly repurposed, as they have already been assessed for safety in man. A key question is how to screen such compounds rapidly and efficiently for activity against new pandemic pathogens such as SARS-CoV-2. Here, we show how a fast and robust computational process can be used to screen large libraries of drugs and natural compounds to identify those that may inhibit the main protease of SARS-CoV-2. We show that the shortlist of 84 candidates with the strongest predicted binding affinities is highly enriched (≥25%) in compounds experimentally validated in vivo or in vitro to have activity in SARS-CoV-2. The top candidates also include drugs and natural products not previously identified as having COVID-19 activity, thereby providing leads for experimental validation. This predictive in silico screening pipeline will be valuable for repurposing existing drugs and discovering new drug candidates against other medically important pathogens relevant to future pandemics.

An adjuvanted subunit SARS-CoV-2 spike protein vaccine provides protection against Covid-19 infection and transmission.

Recombinant protein approaches offer major promise for safe and effective vaccine prevention of SARS-CoV-2 infection. We developed a recombinant spike protein vaccine (called NARUVAX-C19) and characterized its ability when formulated with a nanoemulsion adjuvant to induce anti-spike antibody and T-cell responses and provide protection including against viral transmission in rodent. In mice, NARUVAX-C19 vaccine administered intramuscularly twice at 21-day interval elicited balanced Th1/Th2 humoral and T-cell responses with high titers of neutralizing antibodies against wild-type (D614G) and delta (B.1.617.2) variants. In Syrian hamsters, NARUVAX-C19 provided complete protection against wild-type (D614G) infection and prevented its transmission to naïve animals (n = 2/group) placed in the same cage as challenged animals (n = 6/group). The results contrasted with only weak protection seen with a monomeric spike receptor-binding domain (RBD) vaccine even when formulated with the same adjuvant. These encouraging results warrant the ongoing development of this COVID-19 vaccine candidate.

Artificial Intelligence in Vaccine and Drug Design.

Knowledge in the fields of biochemistry, structural biology, immunological principles, microbiology, and genomics has all increased dramatically in recent years. There has also been tremendous growth in the fields of data science, informatics, and artificial intelligence needed to handle this immense data flow. At the intersection of wet lab and data science is the field of bioinformatics, which seeks to apply computational tools to better understanding of the biological sciences. Like so many other areas of biology, bioinformatics has transformed immunology research leading to the discipline of immunoinformatics. Within this field, many new databases and computational tools have been created that increasingly drive immunology research, in many cases drawing upon artificial intelligence and machine learning to predict complex immune system behaviors, for example, prediction of B cell and T cell epitopes. In this book chapter, we provide an overview of computational tools and artificial intelligence being used for protein modeling, drug screening, vaccine design, and highlight how these tools are being used to transform approaches to pandemic countermeasure development, by reference to the current COVID-19 pandemic.

Computationally repurposed drugs and natural products against RNA dependent RNA polymerase as potential COVID-19 therapies.

Repurposing of existing drugs and drug candidates is an ideal approach to identify new potential therapies for SARS-CoV-2 that can be tested without delay in human trials of infected patients. Here we applied a virtual screening approach using Autodock Vina and molecular dynamics simulation in tandem to calculate binding energies for repurposed drugs against the SARS-CoV-2 RNA-dependent RNA polymerase (RdRp). We thereby identified 80 promising compounds with potential activity against SARS-Cov2, consisting of a mixture of antiviral drugs, natural products and drugs with diverse modes of action. A substantial proportion of the top 80 compounds identified in this study had been shown by others to have SARS-CoV-2 antiviral effects in vitro or in vivo, thereby validating our approach. Amongst our top hits not previously reported to have SARS-CoV-2 activity, were eribulin, a macrocyclic ketone analogue of the marine compound halichondrin B and an anticancer drug, the AXL receptor tyrosine kinase inhibitor bemcentinib. Our top hits from our RdRp drug screen may not only have utility in treating COVID-19 but may provide a useful starting point for therapeutics against other coronaviruses. Hence, our modelling approach successfully identified multiple drugs with potential activity against SARS-CoV-2 RdRp. Supplementary Information: The online version contains supplementary material available at 10.1186/s43556-021-00050-3.

Rapid development of analytical methods for evaluating pandemic vaccines: a COVID-19 perspective.

Vaccines are key in charting a path out of the COVID-19 pandemic. However, development of new vaccines is highly dependent on availability of analytical methods for their design and evaluation. This paper highlights the challenges presented in having to rapidly develop vaccine analytical tools during an ongoing pandemic, including the need to address progressive virus mutation and adaptation which can render initial assays unreliable or redundant. It also discusses the potential of new computational modeling techniques to model and analyze key viral proteins and their attributes to assist vaccine production and assay design. It then reviews the current range of analytical tools available for COVID-19 vaccine application, ranging from in vitro assays for immunogen characterization to assays to measure vaccine responses in vivo. Finally, it provides a future perspective for COVID-19 vaccine analytical tools and attempts to predict how the field might evolve over the next 5-10 years.

Immunisation of ferrets and mice with recombinant SARS-CoV-2 spike protein formulated with Advax-SM adjuvant protects against COVID-19 infection.

The development of a safe and effective vaccine is a key requirement to overcoming the COVID-19 pandemic. Recombinant proteins represent the most reliable and safe vaccine approach but generally require a suitable adjuvant for robust and durable immunity. We used the SARS-CoV-2 genomic sequence and in silico structural modelling to design a recombinant spike protein vaccine (Covax-19™). A synthetic gene encoding the spike extracellular domain (ECD) was inserted into a baculovirus backbone to express the protein in insect cell cultures. The spike ECD was formulated with Advax-SM adjuvant and first tested for immunogenicity in C57BL/6 and BALB/c mice. Covax-19 vaccine induced high spike protein binding antibody levels that neutralised the original lineage B.1.319 virus from which the vaccine spike protein was derived, as well as the variant B.1.1.7 lineage virus. Covax-19 vaccine also induced a high frequency of spike-specific CD4 + and CD8 + memory T-cells with a dominant Th1 phenotype associated with the ability to kill spike-labelled target cells in vivo. Ferrets immunised with Covax-19 vaccine intramuscularly twice 2 weeks apart made spike receptor binding domain (RBD) IgG and were protected against an intranasal challenge with SARS-CoV-2 virus given two weeks after the last immunisation. Notably, ferrets that received the two higher doses of Covax-19 vaccine had no detectable virus in their lungs or in nasal washes at day 3 post-challenge, suggesting that in addition to lung protection, Covax-19 vaccine may have the potential to reduce virus transmission. This data supports advancement of Covax-19 vaccine into human clinical trials.