In vitro and animal models described lower replication capacity and virulence of SARS-CoV-2 Omicron lineage in lower respiratory airways compared to wild type and other variants of concern (oVOCs). Among adult subjects admitted to our hospital (Turin, Italy) due to wild type, oVOCs, and Omicron SARS-CoV-2-related pneumonia (n = 100 for each lineage), the cases of Omicron pneumonia showed lower degree of lung parenchyma involvement (aβ -1.471, p = 0.037), less tendency to parenchyma consolidation (aOR 0.500, p = 0.011), and better respiratory functions (assessed by ambient air arterial blood gas analysis). After adjusting for demographic, previous immunity, and comorbidities, Omicron pneumonia still associated with lower risk of respiratory failure (for severe respiratory failure, Wild-type versus Omicron aOR 15.6, p = 0.005 and oVOCs versus Omicron aOR 31.7, p < 0.001). These observations are in line with preliminary findings from in vitro and animal models and could explain why Omicron infection has been associated with lower mortality and hospitalization in human.
Keywords: ARDS; Omicron; Pneumonia; SARS-CoV-2; Variants of Concern; Virulence.
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