Pulmonary lesions following inoculation with the SARS-CoV-2 Omicron BA.1 (B.1.1.529) variant in Syrian golden hamsters

ABSTRACT

The Omicron BA.1 (B.1.1.529) SARS-CoV-2 variant is characterized by a high number of mutations in the viral genome, associated with immune escape and increased viral spread. It remains unclear whether milder COVID-19 disease progression observed after infection with Omicron BA.1 in humans is due to reduced pathogenicity of the virus or due to pre-existing immunity from vaccination or previous infection. Here, we inoculated hamsters with Omicron BA.1 to evaluate pathogenicity and kinetics of viral shedding, compared to Delta (B.1.617.2) and to animals re-challenged with Omicron BA.1 after previous SARS-CoV-2 614G infection. Omicron BA.1 infected animals showed reduced clinical signs, pathological changes, and viral shedding, compared to Delta-infected animals, but still showed gross- and histopathological evidence of pneumonia. Pre-existing immunity reduced viral shedding and protected against pneumonia. Our data indicate that the observed decrease of disease severity is in part due to intrinsic properties of the Omicron BA.1 variant.

KEYWORDS:

• SARS-CoV-2
• Omicron BA.1
• Delta
• Syrian golden hamster
• pathology
• re-challenge
• pre-existing immunity

Acknowledgements

We thank J.M. Fentener van Vlissingen, Ingeborg van Middelkoop, Rianne Stam, Vincent Duiverman and Vincent Vaes for assistance with the animal studies.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

Conceptualization, B.R., M.R., R.F. B.H.; investigation, M.R., D.N., D.v.R., K.S.S., R.D.d.V, P.v.R., T.K. and B.R.; resources, M.L., C.G.v.K., M.P.G.K.; supervision, B.R., R.D.d.V and B.H.; writing, original draft, B.R., M.R., and B.H.; writing–review and editing, all authors; funding acquisition: M.P.G.K., R.F. B.H., B.R.,

Data and materials availability

Viruses must be obtained through an MTA.

Additional information

Funding

This research is (partly) financed by the NWO Stevin Prize awarded to M.P.G.K. by the Netherlands Organisation for Scientific Research (NWO), and B.L.H., R.A.M.F., B.R., and M.P.G. are supported by the NIH/NIAID Centers of Excellence for Influenza Research and Response (CEIRR) under contract 75N93021C00014-Icahn School of Medicine at Mt. Sinai.