The protease TMPRSS2 facilitates coronavirus infections, yet its mechanism of viral glycoprotein recognition remains unclear. Here we show that, following ACE2 engagement of the SARS-CoV-2 spike (S) inducing the early fusion intermediate conformation (E-FIC), TMPRSS2 cleaves the R815 S2 ' site and promotes fusogenic conformational changes leading to viral entry. We unveil TMPRSS2 recognition of S2 ', identify key residues modulating binding specificity and demonstrate that S2 ' site-directed broadly neutralizing antibodies target E-FIC and inhibit viral entry by blocking TMPRSS2 access. We computationally designed stabilized E-FIC as a vaccine candidate, overcoming the transient nature of this state. We describe a TMPRSS2-directed monoclonal antibody inhibiting several coronaviruses, including SARS-CoV-2 variants and protecting mice against SARS-CoV-2 challenge. These results outline the mechanistic role of TMPRSS2 and S2 ' site-directed antibodies in coronavirus entry.

Coronavirus disease 2019 (COVID-19) is a deadly human viral disease with a high rate of infection, morbidity, and mortality. Although vaccines and antiviral treatments are available, hospitalizations remain steady, and concerns about long-term consequences persist. Therefore, there is a great urgency to develop novel therapies. Here, we analyzed the role of miR-155, one of the most powerful drivers of host antiviral responses including immune and inflammatory responses, in the pathogenicity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Endogenous microRNAs (miRNAs, miRs) are key molecules in preventing viral entry and replication while building an antiviral cellular defense. Our study reveals that miR-155 expression is elevated in patients with COVID-19. Using a mouse model transgenic for human angiotensin-converting enzyme receptor 2, we evaluated the potential of anti-miR-155 therapy. Treating SARS-CoV-2-infected mice with anti-miR-155 significantly reduced miR-155 expression, improved survival, and slightly increased body weight. Notably, these mice showed altered expression of cytokines in the lungs. These findings suggest anti-miR-155 could be a promising therapy to mitigate the cytokine storm and long-lasting symptoms induced by SARS-CoV-2 infection, improving public health outcomes and enhancing global pandemic preparedness.

Research underscores the urgent need for technological innovations to treat lung tissue damage from viral infections and the lasting impact of COVID-19. Our study demonstrates the effectiveness of recombinant human NV1 protein in promoting a pro-healing extracellular matrix that regulates homeostasis in response to excessive tissue reactions caused by infection and injury. NV1 achieves this by calibrating multiple biological mechanisms, including reducing hyperinflammatory cytokine levels (e.g., IFN-γ, TNF-α, IL-10, and IP-10), enhancing the production of proteins involved in viral inactivation and clearance through endocytosis and phagocytosis (e.g., IL-9, IL-1α), regulating pro-clotting and thrombolytic pathways (e.g., downregulates SERPINE 1 and I-TAC during Th1-mediated inflammation), maintaining cell survival under hypoxic conditions via HIF-1α regulation through the M3K5-JNK-AP-1 and TSC2-mTOR pathways, and promoting blood vessel formation. Our findings reveal NV1 as a potential therapeutic candidate for treating severe lung injuries caused by inflammatory and hypoxic conditions from viral infections and related diseases.

Introduction:Staphylococcus aureus is a common gram-positive commensal that, upon entering the bloodstream, can cause devastating illness and death within hours or days. Methicillin-resistant S. aureus (MRSA) infections, now a leading cause of bloodstream infections worldwide, pose significant challenges due to their rapid progression, high mortality rates, and limited therapeutic options. While there are prevalent small animal models of experimental MRSA infection, there has been minimal development of larger mammalian models capable of recapitulating clinical aspects of human systemic MRSA infection. Methods:Following a pilot study to determine the optimal dose and route to establish systemic MRSA infection, we challenged six cynomolgus macaques with 109 colony-forming units MRSA (lineage USA300) via intravenous (IV) route. Animals were monitored closely up to 8 days for physiological, immunological, and cellular endpoints. Histopathology was performed on tissues collected 2 and 8 days after infection. Results:An IV dose of 109 CFU MRSA USA300 in cynomolgus macaques produced bacteremia resulting from multifocal invasive infections, elevated markers of systemic inflammation, as well as weight loss, fever, and hemodynamic changes consistent with bloodstream infection. Hematological analyses demonstrated neutrophilic leukocytosis, lymphocytopenia, monocytosis, and mild thrombocytopenia. We observed a robust cytokine response, including TNF-α, IL-6, G-CSF, and IL-1RA, peaking 6 h post-infection. Flow cytometry immunophenotyping revealed dynamic shifts in circulating monocyte subpopulations, and histopathological analysis demonstrated multi-organ damage with significant findings in the kidneys, heart, liver, and lungs. By 8 days post-infection, moderate to severe myocardial, renal, and hepatic dysfunction were evident, supported by changes in clinical chemistry biomarkers. None of the animals required euthanasia before the scheduled date of termination. Discussion:In this study, we establish a non-human primate model of systemic MRSA infection that allows for the characterization of MRSA pathogenesis and evaluation of therapeutics over a period of days rather than hours. This model successfully recapitulates key aspects of human MRSA bloodstream infections, providing a valuable platform for evaluating therapeutic interventions and understanding disease mechanisms.

IntroductionMost COVID-19 vaccine trials have focused on recipient protection, not protection of their contacts, a critical need. As a subunit intranasal COVID-19 vaccine reduced nasopharyngeal virus more than did an intramuscular (IM) vaccine, we hypothesized that this vaccine might reduce onward transmission to others.MethodsWe vaccinated hamsters with either the IM-administrated licensed mRNA vaccine twice or one dose of mRNA IM followed by adjuvanted subunit intranasal vaccine. 24 hours after SARS-CoV-2 challenge, these animals were housed with naïve recipients in a contactless chamber that allows airborne transmission.ResultsOnward airborne transmission was profoundly blocked: the donor and recipients of the intranasal vaccine-boosted group had lower oral and lung viral loads (VL), which correlated with mucosal ACE2 inhibition activity. Notably, in this head-to-head comparison of COVID-19 booster vaccines on SARS-CoV-2 onward transmission, we found that statistically significant viral reduction in the lung tissues and oral swabs was observed only in the intranasal S1 nanoparticle vaccine-boosted group, but not in the systemic mRNA vaccine-boosted group, suggesting the superior protection of this intranasal vaccine, which could act as an attractive vaccine booster candidate to complement the current licensed systemic vaccines.DiscussionOverall, our study strongly supports the use of the intranasal vaccine as a boost to protect not only the vaccinated person, but also people exposed to the vaccinated person, a key public health goal.

The H5N1 avian influenza virus clade 2.3.4.4b outbreak represents a major pandemic threat for humans, with some reported cases of severe and fatal respiratory illness. A key unanswered question is the pathogenesis of severe H5N1 disease following respiratory infection. In this study, we explored mechanisms of pathogenesis of severe H5N1 disease in cynomolgus and rhesus macaques following infection with the H5N1 isolate A/Texas/37/2024 (huTX37-H5N1). Cynomolgus macaques developed severe pneumonia that was lethal in 100% of macaques by 7 days post-infection. By contrast, rhesus macaques demonstrated dose-dependent mortality, and surviving animals showed protective immunity against high-dose re-challenge. A multi-omics analysis demonstrated that H5N1 infection was characterized by robust induction of proinflammatory cytokines, innate immune cells, complement, coagulation, apoptosis, and immune exhaustion pathways. Taken together, our data indicate inflammation and immune dysregulation as key mechanisms of H5N1 pathogenesis in nonhuman primates.

Marburg virus (MARV) is a filovirus that causes severe and often lethal haemorrhagic fever 1,2 . Despite the increasing frequency of MARV outbreaks, no vaccines or therapeutics are licensed for use in humans. Here we designed mutations that improve the expression, thermostability and immunogenicity of the prefusion MARV glycoprotein (GP) ectodomain trimer, which is the sole target of neutralizing antibodies and vaccines in development 3–8 . We discovered a fully human, pan-marburgvirus monoclonal antibody, MARV16, that broadly neutralizes all MARV isolates, Ravn virus and Dehong virus with 40–100-fold increased potency relative to previously described antibodies 9 . Moreover, MARV16 provided therapeutic protection in guinea pigs challenged with MARV. We determined a cryogenic electron microscopy structure of MARV16-bound MARV GP. The structure shows that MARV16 recognizes a prefusion-specific epitope spanning GP1 and GP2, which blocks receptor binding and prevents conformational changes required for viral entry. We further determined the architecture of the MARV GP glycan cap, which shields the receptor-binding site, and identified architectural similarities with distantly related filovirus GPs. MARV16 and previously identified antibodies directed against the receptor-binding site 9–11 simultaneously bound MARV GP. These antibody cocktails required multiple mutations to escape neutralization by both antibodies, a result that paves the way for the development of MARV therapeutics resistant to viral evolution. MARV GP stabilization along with the discovery of MARV16 advance prevention and treatment options for MARV disease.

Flaviviruses are a family of related viruses that cause substantial global morbidity and mortality. Vaccination against one flavivirus can sometimes exacerbate disease caused by related viruses through antibody-dependent enhancement (ADE) or interfere with the efficacy of subsequent vaccines. To address this challenge, we develop a vaccine strategy by introducing G5C/G102C mutations into the flavivirus envelope (E) glycoprotein. These mutations promote E dimerization through the formation of an inter-chain disulfide bond that conceals the immunodominant and ADE-prone fusion loop epitope (FLE). We validate this design on E proteins from multiple flaviviruses through biochemical, antigenic, and structural analyses. The resulting vaccine candidate, CC_FLE sE, derived from the Zika virus (ZIKV) and formulated with an advanced supramolecular adjuvant, provides significant protection in female mice challenged with ZIKV and prevents ADE caused by a related flavivirus, Dengue virus. In genetically modified mice expressing diverse human immunoglobulin loci, ZIKV CC_FLE sE induces robust neutralizing antibody responses targeting key ZIKV E protein epitopes, including the E-dimer-dependent epitope (EDE), indicating that ZIKV CC_FLE sE can elicit protective antibody responses within the human naïve B cell repertoire. Therefore, CC_FLE sE represents a promising strategy for developing flavivirus vaccines that minimize ADE risk while maintaining high protective efficacy.

The evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in variants that can escape neutralization by therapeutic antibodies. Here, we describe AZD3152, a SARS-CoV-2–neutralizing monoclonal antibody designed to provide improved potency and coverage against emerging variants. AZD3152 binds to the back left shoulder of the SARS-CoV-2 spike protein receptor binding domain and prevents interaction with the human angiotensin-converting enzyme 2 receptor. AZD3152 potently neutralized a broad panel of pseudovirus variants, including the currently dominant Omicron variant JN.1 but has reduced potency against XBB subvariants containing F456L. In vitro studies confirmed F456L resistance and additionally identified T415I and K458E as escape mutations. In a Syrian hamster challenge model, prophylactic administration of AZD3152 protected hamsters from weight loss and inflammation-related lung pathologies and reduced lung viral load. In the phase 1 sentinel safety cohort of the ongoing SUPERNOVA study ( ClinicalTrials.gov : NCT05648110), a single 600-mg intramuscular injection of AZD5156 (containing 300 mg each of AZD3152 and cilgavimab) was well tolerated in adults through day 91. Observed serum concentrations of AZD3152 through day 91 were similar to those observed with cilgavimab and consistent with predictions for AZD7442, a SARS-CoV-2–neutralizing antibody combination of cilgavimab and tixagevimab, in a population pharmacokinetic model. On the basis of its pharmacokinetic characteristics, AZD3152 is predicted to provide durable protection against symptomatic coronavirus disease 2019 caused by susceptible SARS-CoV-2 variants, such as JN.1, in humans.

DNA- based vaccines have demonstrated the potential as a safe and effective modality. PlaCCine, a DNA-based vaccine approach described subsequently relies on a synthetic DNA delivery system and is independent of virus or device. The synthetic functionalized polymer combined with DNA demonstrated stability over 12 months at 4C and for one month at 25C. Transfection efficiency compared to naked DNA increased by 5-15-fold in murine skeletal muscle. Studies of DNA vaccines expressing spike proteins from variants D614G (pVAC15), Delta (pVAC16), or a D614G + Delta combination (pVAC17) were conducted. Mice immunized intramuscular injection (IM) with pVAC15, pVAC16 or pVAC17 formulated with functionalized polymer and adjuvant resulted in induction of spike-specific humoral and cellular responses. Antibody responses were observed after one immunization. And endpoint IgG titers increased to greater than 1x 10 5 two weeks after the second injection. Neutralizing antibodies as determined by a pseudovirus competition assay were observed following vaccination with pVAC15, pVAC16 or pVAC17. Spike specific T cell immune responses were also observed following vaccination and flow cytometry analysis demonstrated the cellular immune responses included both CD4 and CD8 spike specific T cells. The immune responses in vaccinated mice were maintained for up to 14 months after vaccination. In an immunization and challenge study of K18 hACE2 transgenic mice pVAC15, pVAC16 and pVAC17 induced immune responses lead to decreased lung viral loads by greater than 90% along with improved clinical score. These findings suggest that PlaCCine DNA vaccines are effective and stable and further development against emerging SARS-CoV-2 variants is warranted.

In response to the 2022 outbreak of mpox driven by unprecedented human-to-human monkeypox virus (MPXV) transmission, we designed BNT166, aiming to create a highly immunogenic, safe, accessible, and scalable next-generation vaccine against MPXV and related orthopoxviruses. To address the multiple viral forms and increase the breadth of immune response, two candidate multivalent mRNA vaccines were evaluated pre-clinically: a quadrivalent vaccine (BNT166a; encoding the MPXV antigens A35, B6, M1, H3) and a trivalent vaccine (BNT166c; without H3). Both candidates induced robust T cell responses and IgG antibodies in mice, including neutralizing antibodies to both MPXV and vaccinia virus. In challenge studies, BNT166a and BNT166c provided complete protection from vaccinia, clade I, and clade IIb MPXV. Furthermore, immunization with BNT166a was 100% effective at preventing death and at suppressing lesions in a lethal clade I MPXV challenge in cynomolgus macaques. These findings support the clinical evaluation of BNT166, now underway (NCT05988203).

Mayaro virus (MAYV), a mosquito-borne alphavirus, is considered an emerging threat to public health with epidemic potential. Phylogenetic studies show the existence of three MAYV genotypes. In this study, we provide a preliminary analysis of the pathogenesis of all three MAYV genotypes in cynomolgus macaques (Macaca facicularis, Mauritian origin). Significant MAYV-specific RNAemia and viremia were detected during acute infection in animals challenged intravenously with the three MAYV genotypes, and strong neutralizing antibody responses were observed. MAYV RNA was detected at high levels in lymphoid tissues, joint muscle and synovia over 1 month after infection, suggesting that this model could serve as a promising tool in studying MAYV-induced chronic arthralgia, which can persist for years. Significant leucopenia was observed across all MAYV genotypes, peaking with RNAemia. Notable differences in the severity of acute RNAemia and composition of cytokine responses were observed among the three MAYV genotypes. Our model showed no outward signs of clinical disease, but several major endpoints for future MAYV pathology and intervention studies are described. Disruptions to normal blood cell counts and cytokine responses were markedly distinct from those observed in macaque models of CHIKV infection, underlining the importance of developing non-human primate models specific to MAYV infection.

Background Although the mpox global health emergency caused by mpox virus (MPXV) clade IIb.1 has ended, mpox cases are still reported due to low vaccination coverage and waning immunity. COH04S1 is a clinically evaluated, multiantigen COVID-19 vaccine candidate built on a fully synthetic platform of the highly attenuated modified vaccinia Ankara (MVA) vector, representing the only FDA-approved smallpox/mpox vaccine JYNNEOS. Given the potential threat of MPXV resurgence and need for vaccine alternatives, we aimed to assess the capacity COH04S1 and its synthetic MVA (sMVA) backbone to confer MPXV-specific immunity. Methods We evaluated orthopoxvirus-specific and MPXV cross-reactive immune responses in samples collected during a Phase 1 clinical trial of COH04S1 and in non-human primates (NHP) vaccinated with COH04S1 or its sMVA backbone. MPXV cross-reactive immune responses in COH04S1-vaccinated healthy adults were compared to responses measured in healthy subjects vaccinated with JYNNEOS. Additionally, we evaluated the protective efficacy of COH04S1 and sMVA against mpox in mpox-susceptible CAST/EiJ mice. Results COH04S1-vaccinated individuals develop robust orthopoxvirus-specific humoral and cellular responses, including cross-reactive antibodies to MPXV-specific virion proteins as well as MPXV cross-neutralizing antibodies in 45% of the subjects. In addition, NHP vaccinated with COH04S1 or sMVA show similar MPXV cross-reactive antibody responses. Moreover, MPXV cross-reactive humoral responses elicited by COH04S1 are comparable to those measured in JYNNEOS-vaccinated subjects. Finally, we show that mice vaccinated with COH04S1 or sMVA are protected from lung infection following challenge with MPXV clade IIb.1. Conclusions These results demonstrate the capacity of sMVA vaccines to elicit cross-reactive and protective orthopox-specific immunity against MPXV, suggesting that COH04S1 and sMVA could be developed as bivalent or monovalent mpox vaccine alternatives against MPXV.

Introduction Antibody therapeutic strategies have served an important role during the COVID-19 pandemic, even as their effectiveness has waned with the emergence of escape variants. Here we sought to determine the concentration of convalescent immunoglobulin required to protect against disease from SARS-CoV-2 in a Syrian golden hamster model. Methods Total IgG and IgM were isolated from plasma of SARS-CoV-2 convalescent donors. Dose titrations of IgG and IgM were infused into hamsters 1 day prior to challenge with SARS-CoV-2 Wuhan-1. Results The IgM preparation was found to have ~25-fold greater neutralization potency than IgG. IgG infusion protected hamsters from disease in a dose-dependent manner, with detectable serum neutralizing titers correlating with protection. Despite a higher in vitro neutralizing potency, IgM failed to protect against disease when transferred into hamsters. Discussion This study adds to the growing body of literature that demonstrates neutralizing IgG antibodies are important for protection from SARS-CoV-2 disease, and confirms that polyclonal IgG in sera can be an effective preventative strategy if the neutralizing titers are sufficiently high. In the context of new variants, against which existing vaccines or monoclonal antibodies have reduced efficacy, sera from individuals who have recovered from infection with the emerging variant may potentially remain an efficacious tool.

Abstract Background EVUSHELD was developed for the prevention and treatment of mild-to-moderate COVID-19 for high-risk individuals. However, the SARS-CoV-2 virus continues to evolve in the presence of natural- and vaccine-acquired immunity, escaping previously authorized antibody therapies such as bebtelovimab and EVUSHELD. AZD3152 was selected to neutralize all known SARS-CoV-2 variants of concern and is being developed to provide immunocompromised individuals with continued protection against SARS-CoV-2. Methods Structural analyses were performed to map the AZD3152 binding site. Neutralization assays were employed to determine the potency of AZD3152 across a panel of historical and emerging SARS-CoV-2 variants. Hamsters were prophylactically administered 6.7-60 mg/kg AZD3152 or a control antibody, then challenged intranasally with 6x103 PFU WA-1 SARS-CoV-2, then monitored for weight loss; lung viral load and pathology were evaluated at days 3 and 7. A 3 week GLP repeat IM and IV dose toxicity study in nonhuman primates (NHP) was performed. Results AZD3152 binds to a conserved epitope on the spike receptor binding domain and blocks ACE2 binding. AZD3152 potently neutralizes authentic viral variants (EC50 range, 8.3 to 110.9 ng/mL) and SARS-CoV-2 pseudoviruses (EC50 range of 3.2 to 25.0 ng/mL), including XBB.1.5. Prophylactic administration of AZD3152 conferred dose-dependent protection to hamsters following challenge. Even at a suboptimal dose of 6.7 mg/kg, < 5% weight loss and 2 logs reduction in lung viral subgenomic RNA were observed. AZD3152 was not associated with any adverse findings in NHP and the no observed-adverse-effect-level was the highest dose tested (150 mg/kg). Toxicokinetics demonstrated similar systemic exposure following IM and IV dosing with bioavailability of 94.9% and half-life range of 15.2-26.5 days by IM. Conclusion These results demonstrate that AZD3152 binds a conserved epitope resulting in broad neutralization of SARS-CoV-2 variants, protects hamsters from disease, and has a favorable safety profile in NHP. Thus, AZD3152 may serve as a next-generation antibody for the prevention and treatment of COVID-19. Disclosures Joseph R Francica, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Yingyun Cai, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Seme Diallo, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Kim Rosenthal, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Kuishu Ren, BS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Daniel J. Flores, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Andrew Dippel, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Yuling Wu, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Xiaoru Chen, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Erin Cantu, BS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Rakesh Choudhary, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Michal Sulikowski, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Hibret Adissu, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Nydia van Dyk, MSc, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Vaheh Oganesyan, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Saravanan Rajan, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Patricia C. Ryan, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Yueh-Ming Loo, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Taylor Cohen, PhD, AstraZeneca: Employement|AstraZeneca: Stocks/Bonds Mark T. Esser, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Wade Blair, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds

Introduction Adjuvant plays an important role in directing the immune responses induced by vaccines. In previous studies, we have shown that a mucosal SARS-CoV-2 S1 subunit vaccine adjuvanted with a combination of CpG, Poly I:C and IL-15 (named CP15) induced effective mucosal and systemic immunity and conferred nearly sterile protection against SARS-CoV-2 viral replication in macaque models. Methods In this study, we used a hamster model, which mimics the human scenario and reliably exhibits severe SARS-CoV-2 disease similar to hospitalized patients, to investigate the protection efficacy of the vaccines against COVID-19 disease. We compared the weight loss, viral loads (VLs), and clinical observation scores of three different vaccine regimens. All three regimens consisted of priming/boosting with S1 subunit vaccines, but adjuvanted with alum and/or CP15 administrated by either intramuscular (IM) or intranasal (IN) routes: Group 1 was adjuvanted with alum/alum administrated IM/IM; Group 2 was alum-IM/CP15-IN; and Group 3 was CP15-IM/CP15-IN. Results After challenge with SARS-CoV-2 WA strain, we found that the alum/CP15 group showed best protection against weight loss, while the CP15 group demonstrated best reduction of oral SARS-CoV-2 VLs, suggesting that the protection profiles were different. Sex differences for VL and clinical scores were observed. Humoral immunity was induced but not correlated with protection. Moreover, S1-specific binding antibody titers against beta, omicron BA.1, and BA.2 variants showed 2.6-, 4.9- and 2.8- fold reduction, respectively, compared to the Wuhan strain. Discussion Overall, the data suggested that adjuvants in subunit vaccines determine the protection profiles after SARS-CoV-2 infection and that nasal/oral mucosal immunization can protect against systemic COVID-19 disease.

Emerging SARS-CoV-2 Omicron subvariants continue to disrupt COVID-19 vaccine efficacy through multiple immune mechanisms including neutralizing antibody evasion. We developed COH04S1, a synthetic modified vaccinia Ankara vector that co-expresses Wuhan-Hu-1-based spike and nucleocapsid antigens. COH04S1 demonstrated efficacy against ancestral virus and Beta and Delta variants in animal models and was safe and immunogenic in a Phase 1 clinical trial. Here, we report efficacy of COH04S1 and analogous Omicron BA.1- and Beta-specific vaccines to protect Syrian hamsters from Omicron subvariants. Despite eliciting strain-specific antibody responses, all three vaccines protect hamsters from weight loss, lower respiratory tract infection, and lung pathology following challenge with Omicron BA.1 or BA.2.12.1. While the BA.1-specifc vaccine affords consistently improved efficacy compared to COH04S1 to protect against homologous challenge with BA.1, all three vaccines confer similar protection against heterologous challenge with BA.2.12.1. These results demonstrate efficacy of COH04S1 and variant-specific derivatives to confer cross-protective immunity against SARS-CoV-2 Omicron subvariants.

Abstract Background Since the beginning of the COVID-19 pandemic, several variants of concern (VOC) have emerged for which there is evidence of an increase in transmissibility, more severe disease, and/or reduced vaccine effectiveness. Effective COVID-19 vaccine strategies are required to achieve broad protective immunity against current and future VOC. Methods We conducted immunogenicity and challenge studies in macaques and hamsters using a bivalent recombinant vaccine formulation containing the SARS-CoV-2 prefusion-stabilized Spike trimers of the ancestral D614 and the variant Beta strains with AS03 adjuvant (CoV2 preS dTM-AS03) in a primary immunization setting. Results We show that a primary immunization with the bivalent CoV2 preS dTM-AS03 elicits broader and durable (1 year) neutralizing antibody responses against VOC including Omicron BA.1 and BA.4/5, and SARS-CoV-1 as compared to the ancestral D614 or Beta variant monovalent vaccines in naïve non-human primates. In addition, the bivalent formulation confers protection against viral challenge with SARS-CoV-2 prototype D614G strain as well as Alpha and Beta variant strains in hamsters. Conclusions Our findings demonstrate the potential of a Beta-containing bivalent CoV2 preS dTM-AS03 formulation to provide broad and durable immunogenicity, as well as protection against VOC in naïve populations.

During the COVID-19 pandemic, vaccines have produced protective immunity sufficient enough to cause a decrease in hospitalizations and deaths; however, the pandemic continues due to mutational events, predominantly occurring in the S1 sequence of the spike protein of SARS-CoV-2. We have developed a baculovirus-expressed, modified S1 SARS-CoV-2 protein based on the C.1.2 variant, which was first identified in South Africa. 1 This was encapsulated in a vitamin E containing, nonphospholipid liposome, which was then used to subcutaneously immunize Syrian hamsters. This vaccine, when administered at day 1 generates IgG responses that react to the modified C.1.2 S1 protein; full-length spike proteins from Wuhan-Hu-1, Delta, Omicron BA.1; and the Omicron recombinant variant XBB.1.5 in 100% of the animals. The second dose administered subcutaneously on day 28 demonstrated anamnestic response in the quantitative IgG assay to the Wuhan-Hu-1 spike Receptor Binding Domain (RBD). In addition, antibody IgA and IgM responses in sera were demonstrated. Serum IgG antibody responses to the spike proteins of the modified C.1.2 S1 and full-length spike proteins Wuhan-Hu-1, Delta, Omicron BA.1, and Omicron recombinant XBB.1.5 variants are elevated for over 120 days. Challenge of vaccinated and unvaccinated hamsters at day 126 of the study with an Omicron BA.1 resulted in a difference in weight change and viral load based on the qRT-PCR assay seven days after challenge.

The SARS-CoV-2 Omicron (B.1.1.529) variant has proven highly transmissible and has outcompeted the Delta variant in many regions of the world 1 . Early reports have also suggested that Omicron may result in less severe clinical disease in humans. Here we show that Omicron is less pathogenic than prior SARS-CoV-2 variants in Syrian golden hamsters. Infection of hamsters with the SARS-CoV-2 WA1/2020, Alpha, Beta, or Delta strains led to 4-10% weight loss by day 4 and 10-17% weight loss by day 6, as expected 2,3 . In contrast, infection of hamsters with two different Omicron challenge stocks did not result in any detectable weight loss, even at high challenge doses. Omicron infection still led to substantial viral replication in both the upper and lower respiratory tracts and pulmonary pathology, but with a trend towards higher viral loads in nasal turbinates and lower viral loads in lung parenchyma compared with WA1/2020 infection. These data suggest that the SARS-CoV-2 Omicron variant may result in more robust upper respiratory tract infection but less severe lower respiratory tract clinical disease compared with prior SARS-CoV-2 variants.