Vero76 cells. The inhibitory effects of G13-CRD against two authentic SARS-CoV-2 viruses, Wuhan Hu-1 (wild type), and Omicron BA.1, were investigated (SI, Section 7). Sotrovimab, a clinically approved monoclonal antibody for Covid-19 treatment was analyzed as a control. G13-CRD100 was highly potent against the wild-type virus, resulting in ~92% inhibition at 0.1 nM (equivalent to ~9 pM EC50 for non-cooperative inhibition, n = 1) and complete inhibition at 10 nM (Fig. ). In contrast, Sotrovimab was less effective, showing apparently no inhibition at 0.1 nM, although significant inhibition was observed at 1 nM (~85%) and above. The inhibition data of authentic viruses did not follow the classical potency-dose dependence, and the potency increased more rapidly with dose once inhibition was observed, making it difficult to fit the data with inhibition models to derive EC50 values. Against Omicron variant BA.1, both Sotrovimab and G13-CRD100 showed reduced efficacy and significant inhibition was observed at 5 nM and 10nM, respectively but both completely inhibited infection at 25nM. Importantly, the G13-OH control gave no inhibition across the whole concentration range tested, confirming that G13-CRD's inhibitory effect originates from specific CRD-glycan interactions, as expected. As S protein glycosylation sites are conserved in all four SARS-CoV-2 variants (and in fact in all variants of concern identified by WHO to date), individual G13-CRD-S protein interactions are thus expected to be similar across the different variants. The fact that all four viral variants were, in the pseudotype model, consistently neutralized by G13-CRD with comparable EC50 and identical n (= 1) matches well with this expectation. This result implies that these different particles may have exhibited similar numbers of S proteins and inter-S-protein spacing, allowing them to interact with G13-CRD in a similar way. A large potency difference for G13-CRD against the authentic-over pseudo-Wuhan variant (Hu-1) could thus be assigned to differences in virion size/shape (~95 nm sphere, vs. ~80 nm x 170 nm bullet-shaped ), number of S-proteins, and inter-S-protein spacing. While individual S-protein-G13-CRD interactions may be similar, differences in inter-S-protein spacing and surface curvature will affect G13-CRD's ability to crosslink neighboring S proteins on the virion surface, which is critical to interrupt S-protein conformational changes and membrane fusion, and thus viral infection. In fact, our G13-CRD was designed to target the inter-S protein spacing (~30 nm, see SI, Section 8) of the Wuhan wild-type Hu-1 based on its cryo-EM structure (i.e. ~40 spikes randomly distributed on a spherical virion of ~95 nm), and it exhibited a great potency against this virus (~9 pM equivalent EC50). These results clearly demonstrate the great potential of our design strategy for G13-CRD-based antivirals. The lower potency of Sotrovimab against the authentic BA.1 over Wuhan Hu-1 variant is assigned to immune evasion mutations of S proteins in BA.1, which weakened Sotrovimab's binding affinity and hence neutralizing potency. This result is fully consistent with the significantly reduced potencies observed for most neutralizing Abs and sera from past infections and/or vaccinations against the Omicron variant over wild-type Hu-1. As G13-CRD's antiviral action is binding to S protein glycans to block viral entry, it was expected to exhibit similar potencies against both the authentic BA.1 and Wuhan Hu-1 variants as their S-protein glycans are conserved. However, our results show this is not the case, implying that BA.1 variant must have evolved other ways (besides immune evasion mutations in S proteins) which evade neutralization by multivalent inhibitors, such as G13-CRD. A likely mechanism here is altering the number of S proteins (hence inter-S-protein spacing) incorporated into virion particles, making our current G13-CRD no longer spatially matched to crosslink neighboring S proteins to exert potent neutralization. This is supported by the observation that a potent anti-Ebola virus antibody indeed cross-links neighboring S proteins via its two Fab arms in cryo-electron tomography. Unfortunately, the cryo-EM structure of whole authentic Omicron variant with intact S proteins remains to be reported. We therefore call for urgent comparative cryo-EM analysis of authentic SARS-CoV-2 variants with intact S proteins, including the Omicron variant, to help the design of spatially-matched PNLs for potent, specific neutralisation of each SARS-CoV-2 variant.