Replication Kinetics of B.1.351 and B.1.1.7 SARS-CoV-2 Variants of Concern Including Assessment of a B.1.1.7 Mutant Carrying a Defective ORF7a Gene

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiological agent of COVID-19, is a readily transmissible and potentially deadly pathogen which is currently re-defining human susceptibility to pandemic viruses in the modern world. The recent emergence of several genetically distinct descendants known as variants of concern (VOCs) is further challenging public health disease management, due to increased rates of virus transmission and potential constraints on vaccine effectiveness. We report the isolation of SARS-CoV-2 VOCs imported into Australia belonging to the B.1.351 lineage, first described in the Republic of South Africa (RSA), and the B.1.1.7 lineage originally reported in the United Kingdom, and directly compare the replication kinetics of these two VOCs in Vero E6 cells. In this analysis, we also investigated a B.1.1.7 VOC (QLD1516/2021) carrying a 7-nucleotide deletion in the open reading frame 7a (ORF7a) gene, likely truncating and rendering the ORF7a protein of this virus defective. We demonstrate that the replication of the B.1.351 VOC (QLD1520/2020) in Vero E6 cells can be detected earlier than the B.1.1.7 VOCs (QLD1516/2021 and QLD1517/2021), before peaking at 48 h post infection (p.i.), with significantly higher levels of virus progeny. Whilst replication of the ORF7a defective isolate QLD1516/2021 was delayed longer than the other viruses, slightly more viral progeny was produced by the mutant compared to the unmutated isolate QLD1517/2021 at 72 h p.i. Collectively, these findings contribute to our understanding of SARS-CoV-2 replication and evolutionary dynamics, which have important implications in the development of future vaccination, antiviral therapies, and epidemiological control strategies for COVID-19.

Antiviral and Immunomodulatory Effects of Pelargonium sidoides DC. Root Extract EPs® 7630 in SARS-CoV-2-Infected Human Lung Cells

“…We found substantial inhibition of SARS-CoV-2 VOC propagation, comparable to the original Munich patient isolate in Calu-3 cells using 100 μg/ml EPs 7630 ( Supplementary Figure S1A ). At low concentrations of 10 μg/ml EPs 7630, we did not detect a significant reduction of viral RNA levels, possibly as a consequence of increased replicative fitness reported for the analyzed VOCs ( Pyke et al, 2021 ; Rosenke et al, 2021 ; Touret et al, 2021 ). To exclude unspecific EPs 7630-induced inhibitory effects in Calu-3 cells, virus growth of other enveloped viruses, specifically mumps virus (MuV) and a Rift Valley fever virus (RVFV) clone 13-based reporter virus ( Kuri et al, 2010 ) was tested in the absence and presence of EPs 7630 ( Supplementary Figure S1B ).…”

“…In addition, EPs 7630 treatment efficiently reduced SARS-CoV-2 RNA levels in human lung cells infected with VOCs Alpha and Beta, highlighting its broadly-acting antiviral activity and the potential to inhibit newly emerging SARS-CoV-2 variants in the future. Although we detected reduced inhibition of VOC propagation at low concentrations, possibly due to the reported increase of replicative fitness for SARS-CoV-2 Alpha and Beta (Pyke et al, 2021;Rosenke et al, 2021;Touret et al, 2021), the broadly acting antiviral effects of EPs 7630 were clearly retained.…”

Effects of Spike Mutations in SARS-CoV-2 Variants of Concern on Human or Animal ACE2-Mediated Virus Entry and Neutralization

“…Our replication kinetics study using parental (lineage A), B.1, Alpha (B.1.1.7) and Beta (B.1.351) SARS-CoV-2 variants in CRFK cells stably expressing human ACE2 or hamster ACE2 revealed a comparatively higher replicative capacity of the Beta variant. This is consistent with the report of increased replication efficiency of Beta variant over Alpha variant in Vero cells [66]. In our experimental infection study using hamsters infected with parental virus (lineage A), Alpha (B.1.1.7) and Beta (B.1.351) VOC, more robust viral replication was observed in the nasal washes with the Beta VOC than the prototype virus or the Alpha VOC at 3 DPC, although the Beta variant inoculum titer was significantly lower than the inoculum dose of the other two viruses.…”

Isolation and characterization of SARS-CoV-2 Beta variant from UAE travelers

“…It is the subject of further exploration, whether the acquired mutations and in vitro/in vivo replication dynamics of Beta variant correlate with higher rate of transmissibility compared to other variants of concern. Pyke et al, have demonstrated quick replication of the Beta variant peaking at 48 hours post infection with considerably higher levels of virus replication compared to Alpha variant [ 25 ]. Apparently, the affinity of Beta RBD binding to ACE2 receptors is also found to be 2.7 fold higher than that of Alpha variant [ 26 , 27 ].…”