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Published on: January 9, 2018
Reduced pathogenicity of the SARS-CoV-2 omicron variant in hamsters
Katherine McMahan1, Victoria Giffin1, Lisa H Tostanoski1
1Center for Virology and Vaccine Research, Beth Israel Deaconess Medical Center, Boston, MA, USA.
Background:
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron (B.1.1.529) variant has proven to be highly transmissible and has outcompeted the Delta variant in many regions of the world. Early reports have also suggested that Omicron may result in less severe clinical disease in humans. Here, we show that Omicron is less pathogenic than prior SARS-CoV-2 variants in Syrian golden hamsters.
Methods:
Hamsters were inoculated with either SARS-CoV-2 Omicron or other SARS-CoV-2 variants. Animals were followed for weight loss, and upper and lower respiratory tract tissues were assessed for viral loads and histopathology.
Findings:
Infection of hamsters with the SARS-CoV-2 WA1/2020, Alpha, Beta, or Delta strains led to 4%-10% weight loss by day 4 and 10%-17% weight loss by day 6. In contrast, infection of hamsters with two different Omicron challenge stocks did not result in any detectable weight loss, even at high challenge doses. Omicron infection led to substantial viral replication in both the upper and lower respiratory tracts but demonstrated lower viral loads in lung parenchyma and reduced pulmonary pathology compared with WA1/2020 infection.
Conclusions:
These data suggest that the SARS-CoV-2 Omicron variant may result in robust upper respiratory tract infection, but less severe lower respiratory tract clinical disease, compared with prior SARS-CoV-2 variants.
Funding:
Funding for this study was provided by NIH grant CA260476, the Massachusetts Consortium for Pathogen Readiness, the Ragon Institute, and the Musk Foundation.
Insights
The Omicron variant of SARS-CoV-2 causes less severe disease in hamsters than previous variants. Omicron infection leads to robust upper respiratory infection but reduced lung pathology, indicating lower pathogenicity.
Area of Science:
- Virology
- Infectious Diseases
- Pathology
Background:
- The SARS-CoV-2 Omicron variant (B.1.1.529) is highly transmissible and has replaced the Delta variant globally.
- Emerging evidence suggests Omicron may cause less severe illness in humans.
- This study investigates the pathogenicity of Omicron compared to previous SARS-CoV-2 variants.
Purpose of the Study:
- To compare the pathogenicity of the SARS-CoV-2 Omicron variant with prior SARS-CoV-2 variants.
- To assess clinical disease severity, viral loads, and histopathology in a hamster model.
Main Methods:
- Syrian golden hamsters were inoculated with Omicron or other SARS-CoV-2 variants.
- Animals were monitored for weight loss.
- Upper and lower respiratory tract tissues were analyzed for viral loads and histopathological changes.
Main Results:
- Omicron infection did not cause significant weight loss in hamsters, unlike other variants (WA1/2020, Alpha, Beta, Delta).
- Omicron replicated in both upper and lower respiratory tracts.
- Reduced viral loads and pulmonary pathology were observed in the lungs of Omicron-infected hamsters compared to WA1/2020.
Conclusions:
- The SARS-CoV-2 Omicron variant demonstrates lower pathogenicity in Syrian golden hamsters compared to previous variants.
- Omicron infection results in significant upper respiratory tract replication but less severe lower respiratory tract disease.
- These findings support early clinical observations of reduced disease severity associated with the Omicron variant.
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