Real-life Evidence of Lower Lung Virulence in COVID-19 Inpatients Infected with SARS-CoV-2 Omicron Variant Compared to Wild-Type and Delta SARS-CoV-2 Pneumonia

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 (a beta -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.

Automated summary

In vitro and animal models have shown that the SARS-CoV-2 Omicron lineage has lower replication capacity and virulence in the lower respiratory airways compared to the wild type and other variants of concern. Clinical observations of adult patients with Omicron pneumonia in our hospital in Turin, Italy also demonstrated lower lung involvement, less tendency to lung consolidation, and better respiratory function compared to wild type and other variants. Adjusted for demographic factors, previous immunity, and comorbidities, Omicron pneumonia was still associated with a lower risk of respiratory failure compared to wild type and other variants. These findings are consistent with in vitro and animal model studies and may explain why Omicron infection has been associated with lower mortality and hospitalization in humans.