Comparison of Plaque Size, Thermal Stability, and Replication Rate among SARS-CoV-2 Variants of Concern.

Seong-Jun Kim,Insu Hwang,Hyun Woo Moon,Dae-Gyun Ahn,Gun Young Yoon,Chonsaeng Kim,Haesoo Kim,Bum-Tae Kim,Kyun-Do Kim,Wooseong Lee,Young-Chan Kwon,Gi Uk Jeong

doi:10.3390/v14010055

Abstract

SARS-CoV-2, like other RNA viruses, has a propensity for genetic evolution owing to the low fidelity of its viral polymerase. Several recent reports have described a series of novel SARS-CoV-2 variants. Some of these have been identified as variants of concern (VOCs), including alpha (B.1.1.7, Clade GRY), beta (B.1.351, Clade GH), gamma (P.1, Clade GR), and delta (B.1.617.2, Clade G). VOCs are likely to have some effect on transmissibility, antibody evasion, and changes in therapeutic or vaccine effectiveness. However, the physiological and virological understanding of these variants remains poor. We demonstrated that these four VOCs exhibited differences in plaque size, thermal stability at physiological temperature, and replication rates. The mean plaque size of beta was the largest, followed by those of gamma, delta, and alpha. Thermal stability, evaluated by measuring infectivity and half-life after prolonged incubation at physiological temperature, was correlated with plaque size in all variants except alpha. However, despite its relatively high thermal stability, alpha’s small plaque size resulted in lower replication rates and fewer progeny viruses. Our findings may inform further virological studies of SARS-CoV-2 variant characteristics, VOCs, and variants of interest. These studies are important for the effective management of the COVID-19 pandemic.

Highlights

Several novel variants of SARS-CoV-2 have been identified since the COVID-19 pandemic began in December 2019
The World Health Organization identifies novel SARS-CoV-2 variants of concern (VOCs) based on their potential impact on public health, according to evidence of enhanced transmissibility, increased severity, reduced antibody neutralization arising from former infection or vaccination, detection evasion ability, or decreased treatment or vaccine efficacy [3]
We noted that each of these variants presented with different plaque sizes in Vero E6 cells (Figure 1A)

Summary

Introduction

Several novel variants of SARS-CoV-2 have been identified since the COVID-19 pandemic began in December 2019. The World Health Organization identifies novel SARS-CoV-2 variants of concern (VOCs) based on their potential impact on public health, according to evidence of enhanced transmissibility, increased severity, reduced antibody neutralization arising from former infection or vaccination, detection evasion ability, or decreased treatment or vaccine efficacy [3]. There are currently only four circulating SARS-CoV-2 VOCs: alpha (B.1.1.7, clade GRY), beta (B.1.351, clade GH), gamma (P.1, clade GR), and delta (B.1.617.2, clade G). They share D614G mutation, conferring increased infectivity, likely due to changes affecting the receptor binding and fusion [4,5,6,7]. Alpha requires the most force to be detached from the receptor, followed by beta/gamma and delta [10]

Methods

Results

Conclusion