The Omicron variant displays reduced ability to cause disease compared to the Delta variant and an ancestral SARS-CoV-2 strain in a hamster model, according to data presented in a paper, peer reviewed and recently accepted for publication in Nature on February 1, 2022.
A team of researchers led by Kei Sato, Associate Professor at The Institute of Medical Science, The University of Tokyo and colleagues first investigated the ability of Omicron to fuse with human cells compared to Delta and an ancestral SARS-CoV-2 variant (B.1.1) in a cell-based fusion assay, and found that Omicron displayed lower cell fusion compared to the controls. They suggest this may be due to poor spike protein cleavage efficacy, which facilitates cell fusion, in the Omicron variant.
The researchers then investigated the pathogenicity of Omicron in a hamster model. Hamsters infected with Omicron exhibited significantly decreased weight-loss compared to hamsters infected with Delta and ancestral SARS-CoV-2, although they did display significant weight-loss compared to uninfected hamsters. Omicron-infected hamsters also showed less impaired lung-function compared to those infected with the other variants, and on some measures, such as subcutaneous oxygen saturation (SpO2), compared favourably to uninfected hamsters. Omicron-infected hamsters also displayed significantly fewer lung lesions than hamsters infected with other variants.
The researchers also investigated viral production by collecting daily oral swabs from infected hamsters. They observed that Delta and ancestral SARS-CoV-2-infected hamsters saw the greatest viral replication one day post infection, with high levels of viral RNA maintained for a week. In contrast, Omicron-infected hamsters displayed peaks of viral replication at two to three days post infection, after which viral RNA loads rapidly declined.
Original Article
Rigel Suzuki, Daichi Yamasoba, Izumi Kimura, Lei Wang, Mai Kishimoto, Jumpei Ito, Yuhei Morioka, Naganori Nao, Hesham Nasser, Keiya Uriu, Yusuke Kosugi, Masumi Tsuda, Yasuko Orba, Michihito Sasaki, Ryo Shimizu, Ryoko Kawabata, Kumiko Yoshimatsu, Hiroyuki Asakura, Mami Nagashima, Kenji Sadamasu, Kazuhisa Yoshimura, The Genotype to Phenotype Japan (G2P-Japan) Consortium, Hirofumi Sawa, Terumasa Ikeda, Takashi Irie, Keita Matsuno, Shinya Tanaka, Takasuke Fukuhara & Kei Sato. 1 February 2022. Attenuated fusogenicity and pathogenicity of SARS-CoV-2 Omicron variant. Nature.DOI: 10.1038/s41586-022-04462-1
URL: https://www.nature.com/articles/s41586-022-04462-1
Time-course dynamics of Omicron in vivo.
Syrian hamsters were intranasally inoculated with saline (n = 6, uninfected control), an ancestral SARS-CoV-2 variant B.1.1 (n = 6), Delta (n = 6) and Omicron (n = 6). Six hamsters of the same age were mock infected. Body weight (left), Penh (the second from the left), Rpef (the second from the right), SpO2 (right) were routinely measured. Data are the average ± s.e.m. Overall, statistically significant dif-ferences versus B.1.1 and Delta through timepoints were determined by multiple regression.
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Associate Professor Kei SatoDivision of Systems Virology, The Institute of Medical Science, The University of Tokyo
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