Pathogenicity, transmissibility, and fitness of SARS-CoV-2 Omicron in Syrian hamsters
Shuofeng Yuan, Zi‐Wei Ye, Ronghui Liang, Kaiming Tang, Jinxia Zhang, Gang Lu, Chon Phin Ong, Vincent Kwok‐Man Poon, Chris Chung‐Sing Chan, Bobo Wing-Yee Mok, Zhenzhi Qin, Yubin Xie, Allen Wing‐Ho Chu, Wan-Mui Chan, Jonathan Daniel Ip, Haoran Sun, Jessica Oi‐Ling Tsang, Terrence Tsz‐Tai Yuen, Kenn Ka‐Heng Chik, Chris Chun-Yiu Chan, Jian‐Piao Cai, Cuiting Luo, Lu Lu, Cyril Chik‐Yan Yip, Hin Chu, Kelvin Kai‐Wang To, Honglin Chen, Dong‐Yan Jin, Kwok-Yung Yuen, Jasper Fuk‐Woo Chan
Abstract
The in vivo pathogenicity, transmissibility, and fitness of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron (B.1.1.529) variant are not well understood. We compared these virological attributes of this new variant of concern (VOC) 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 and chemokine dysregulation, and lung damage than Delta-infected hamsters. Both variants were highly transmissible through contact transmission. In noncontact transmission studies Omicron demonstrated similar or higher transmissibility than Delta. Delta outcompeted Omicron without selection pressure, but this scenario 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 therefore urgently needed.