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.

Differences in neuroinflammation in the olfactory bulb between D614G, Delta and Omicron BA.1 SARS-CoV-2 variants in the hamster model

“…Within the affected olfactory epithelium and lamina propria predominantly neutrophilic infiltrates were present, whereas the associated turbinates’ lumina contained substantial mucopurulent exudates. As reported by Rissmann et al (Rissmann et al, 2022), the hamsters infected with Delta showed more inflammation compared to Omicron BA.1 infected hamsters, which showed the least inflammatory lesions within the olfactory mucosa.…”

“…The hamster model has been proven useful to study the pathogenesis of respiratory disease caused by SARS-CoV-2 infection for different variants (Bryche et al, 2020; Frere et al, 2022; de Melo et al, 2021; Rissmann et al, 2022; Sia et al, 2020; Zazhytska et al, 2022). This study suggests that the neuroinvasiveness and neurovirulence of different SARS-CoV-2 variants can also be studied in the hamster model.…”

The Omicron variant of concern: Diversification and convergent evolution in spike protein, and escape from anti-Spike monoclonal antibodies

“…In this regard, VOC Beta( Ravi et al, 2021 ) and Gamma ( Montagutelli et al, 2021 ) could establish infection in wild-type mice, but with a milder infection than in human ACE2 transgenic mice ( Tarres-Freixas et al, 2021 ). Omicron, because of its ability to infect mice ( Bentley et al, 2021 , Liu et al, 2022 , Rissmann et al, 2022 , Suryawanshi et al, 2022 ), was hypothesized to emerge from partially fit jump species( Wei et al, 2021 ), and reversions after widespread circulation in humans could support such hypothesis. The F486V mutation found in BA.4/5 facilitates escape from certain Class 1 and Class 2 antibodies to the RBD but compromises the Spike affinity for the cellular receptor ACE2, but the R493Q reversion mutation restores receptor affinity, and consequently, the fitness of BA.4/5 ( Wang et al, 2022a ).…”