Vaccines play a critical role in combating the COVID-19 pandemic. Future control of the pandemic requires improved vaccines with high efficacy against newly emerging SARS-CoV-2 variants and the ability to reduce virus transmission. Here we compare immune responses and preclinical efficacy of the mRNA vaccine BNT162b2, the adenovirus-vectored spike vaccine Ad2-spike and the live-attenuated virus vaccine candidate sCPD9 in Syrian hamsters, using both homogeneous and heterologous vaccination regimens. Comparative vaccine efficacy was assessed by employing readouts from virus titrations to single-cell RNA sequencing. Our results show that sCPD9 vaccination elicited the most robust immunity, including rapid viral clearance, reduced tissue damage, fast differentiation of pre-plasmablasts, strong systemic and mucosal humoral responses, and rapid recall of memory T cells from lung tissue after challenge with heterologous SARS-CoV-2. Overall, our results demonstrate that live-attenuated vaccines offer advantages over currently available COVID-19 vaccines.

The development of effective SARS-CoV-2 vaccines has been essential to control COVID-19, but significant challenges remain. One problem is intramuscular administration, which does not induce robust mucosal immune responses in the upper airways—the primary site of infection and virus shedding. Here we compare the efficacy of a mucosal, replication-competent yet fully attenuated virus vaccine, sCPD9-ΔFCS, and the monovalent mRNA vaccine BNT162b2 in preventing transmission of SARS-CoV-2 variants B.1 and Omicron BA.5 in two scenarios. Firstly, we assessed the protective efficacy of the vaccines by exposing vaccinated male Syrian hamsters to infected counterparts. Secondly, we evaluated transmission of the challenge virus from vaccinated and subsequently challenged male hamsters to naïve contacts. Our findings demonstrate that the live-attenuated vaccine (LAV) sCPD9-ΔFCS significantly outperformed the mRNA vaccine in preventing virus transmission in both scenarios. Our results provide evidence for the advantages of locally administered LAVs over intramuscularly administered mRNA vaccines in preventing infection and reducing virus transmission.

Severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) has developed substantial antigenic variability. As the majority of the population now has pre-existing immunity due to infection or vaccination, the use of experimentally generated animal immune sera can be valuable for measuring antigenic differences between virus variants. Here, we immunized Syrian hamsters by two successive infections with one of nine SARS-CoV-2 variants. Their sera were titrated against 16 SARS-CoV-2 variants, and the resulting titers were visualized using antigenic cartography. The antigenic map shows a condensed cluster containing all pre-Omicron variants (D614G, Alpha, Delta, Beta, Mu, and an engineered B.1+E484K variant) and considerably more diversity among a selected panel of Omicron subvariants (BA.1, BA.2, BA.4/BA.5, the BA.5 descendants BF.7 and BQ.1.18, the BA.2.75 descendant BN.1.3.1, the BA.2-derived recombinants XBB.2 and EG.5.1, and the BA.2.86 descendant JN.1). Some Omicron subvariants were as antigenically distinct from each other as the wildtype is from the Omicron BA.1 variant. Compared to titers measured in human sera, titers in hamster sera are of higher magnitude, show less fold change, and result in a more compact antigenic map topology. The results highlight the potential of sera from hamsters for the continued antigenic characterization of SARS-CoV-2.

The open reading frame 3a (ORF3a) is a protein important to the pathogenicity of SARS-CoV-2. The cytoplasmic domain of ORF3a has three canonical tyrosine-based sorting signals (160YNSV163, 211YYQL213, and 233YNKI236), and a previous study has indicated that mutation of the 160YNSV163 motif abrogated plasma membrane expression and inhibited ORF3a-induced apoptosis. Here, we have systematically removed all three tyrosine-based motifs and assessed the importance of each motif or combination of motifs in trafficking to the cell surface. Our results indicate that the 160YNSV163 motif alone was insufficient for ORF3a cell-surface trafficking, while the 211YYQL213 motif was the most important. Additionally, an ORF3a with all three YxxΦ motifs disrupted (ORF3a-[ΔYxxΦ]) was not transported to the cell surface, and LysoIP studies indicate that ORF3a but not ORF3a-[ΔYxxΦ] was present in late endosome/lysosome fractions. A growth-curve analysis of different SARS-CoV-2 viruses expressing the different mutant ORF3a proteins revealed no significant differences in virus replication. Finally, the inoculation of K18hACE-2 mice indicated that the SARS-CoV-2 lacking the three YxxΦ motifs was less pathogenic than the unmodified SARS-CoV-2. These results indicate that the tyrosine motifs of ORF3a contribute to cell-surface expression and SARS-CoV-2 pathogenesis

How SARS-CoV-2 Omicron evolved remains obscure. T492I, an Omicron-specific mutation encountered in SARS-CoV-2 nonstructural protein 4 (NSP4), enhances viral replication and alters nonstructural protein cleavage, inferring potentials to drive evolution. Through evolve-and-resequence experiments of SARS-CoV-2 wild-type (hCoV-19/USA/WA-CDC-02982585-001/2020, A) and Delta strains (B.1.617) with or without T492I, this study demonstrates that the NSP4 mutation T492I confers accelerated phenotypic adaption and a predisposition to the emergence of SARS-CoV-2 Omicron-like variants. The T492I-driven evolution results in accelerated enhancement in viral replication, infectivity, immune evasion capacity, receptor-binding affinity and potential for cross-species transmission. Aside from elevated mutation rates and impact on deaminases, positive epistasis between T492I and adaptive mutations could potentially mechanistically facilitate the shifts in mutation spectra and indirectly determines the Omicron-predisposing evolution. These suggest a potentially important role of the driver mutation T492I in the evolution of SARS-CoV-2 Omicron variants. Our findings highlight the existence and importance of mutation-driven predisposition in viral evolution.

3D nanosystems equipped with polysulfates as binding sites are effective virus inhibitors due to their ability to dynamically deform while adhering to a virus. Here, a new supramolecular nanosystem assembled from a block copolymer consisting of sulfated linear polyglycerol and polytrimethylene carbonate is presented. It exhibits a unique morphology, 100 nm sized spheres with a distinct brush‐like corona. The negatively charged sulfates are distributed on the outer shell and enable exceptional homogeneity of the particles, thereby enhancing the efficiency of multivalent interactions. Various sulfation levels are tested and demonstrated extremely low half‐maximal inhibition concentration (IC ₅₀ ) values in plaque reduction assays tested on herpes simplex virus type‐1 (HSV‐1): 0.43, 0.16, and 0.037 µg mL ⁻¹ of the 45%, 76% and 100% sulfated assemblies, respectively. Using cryo electron microscopy (cryo‐EM), viruses trapped are observed by multiple layers of the nano‐assemblies. Both 76% and 100% sulfated assemblies show therapeutic potential in the post‐infection model. The inhibitory behavior of the 76% and 100% sulfated assemblies is further confirmed against Omicron infection. This work demonstrates that the presented 3D flexible nano‐assemblies can block the virus entry into the host cells with superior morphology and efficiency, establishing them as a promising candidate for antiviral applications.