The in vivo pathogenicity, transmissibility, and fitness of the SARS-CoV-2 Omicron (B.1.1.529) variant are unclear. We compared these virological attributes of this new variant of concern with those of the Delta (B.1.617.2) variant in a Syrian hamster model of COVID-19. Omicron-infected hamsters lost significantly less body weight and exhibited reduced clinical scores, respiratory tract viral burdens, cytokine/chemokine dysregulation, and lung damage than Delta-infected hamsters. Both variants were highly transmissible via contact transmission. In non-contact transmission studies, Omicron demonstrated similar or higher transmissibility than Delta. Delta outcompeted Omicron without selection pressure. This scenario drastically changed once immune selection pressure with neutralizing antibodies active against Delta but poorly active against Omicron was introduced. Next-generation vaccines and antivirals effective against this new VOC are urgently needed.

中文翻译：

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SARS-CoV-2 Omicron 在叙利亚仓鼠中的致病性、传播性和适应性

SARS-CoV-2 Omicron (B.1.1.529) 变体的体内致病性、传播性和适应性尚不清楚。我们在叙利亚仓鼠 COVID-19 模型中将这种受关注的新变体的这些病毒学属性与 Delta (B.1.617.2) 变体的病毒学属性进行了比较。与感染 Delta 的仓鼠相比，感染 Omicron 的仓鼠体重明显减轻，临床评分、呼吸道病毒负荷、细胞因子/趋化因子失调和肺损伤明显减少。两种变体都通过接触传播高度传播。在非接触传播研究中，Omicron 表现出与 Delta 相似或更高的传播能力。Delta 在没有选择压力的情况下击败了 Omicron。一旦引入了免疫选择压力，其中和抗体对 Delta 有活性，但对 Omicron 的活性很差，这种情况就发生了巨大的变化。迫切需要对这种新型 VOC 有效的下一代疫苗和抗病毒药物。