Written by: Dr. Ali Khatau
Posted at: 2022-02-12 19:38:29
Early reports following the emergence of the Omicron variant suggest that the variant is more likely to cause less severe illness than previous variants of SARS-CoV-2. Sequencing of the Omicron genome suggested that this variant carries a large number of mutations, including on the spike protein. The large number of mutations carried by Omicron could be a potential reason for this reduction in illness severity. However, the milder disease due to an Omicron infection could also be a result of a person’s enhanced immunity, acquired due to vaccination or past SARS-CoV-2 infections. Although an increase in immunity may influence the severity of illness, studies in animals and cells cultured in the laboratory suggest that the mutations carried by the Omicron variant have made it less efficient at infecting the lungs than the Delta variant. This could explain the less severe illness that the Omicron variant causes. The SARS-CoV-2 virus can affect both the upper and lower respiratory tracts. The upper respiratory tract consists of the nose, sinuses, and throat, whereas the lower respiratory tract includes the trachea and the lungs. Severe illness due to the wild-type SARS-CoV-2 and the previous variants often involves the infection and inflammation of the lungs. Inflammation can cause fluid to accumulate in the air sacs, or alveoli, in the lungs, reducing the capacity of the lungs to transfer oxygen to the blood. Scientists have conducted experiments using animal models and laboratory cultures of lung cells to characterize the ability of Omicron to infect the respiratory tract and cause severe illness. This includes a study carried out at the University of Hong Kong that used human lung cells cultured in the laboratory, to analyze the ability of the Omicron variant to infect the lungs. These cells were cultured from lung tissue removed during treatment of the lung. In the study, Omicron replicated 70 times faster than Delta in the human bronchi, which are the tubes connecting the trachea with the lungs. However, it was less efficient at replicating in the lung tissue than Delta and the wild-type SARS-CoV-2. In sum, these studies show that Omicron may be less efficient at infecting the lungs. Consistent with this, there is growing evidence suggesting that people with an Omicron infection are less likely to be hospitalized or to require intensive care unit admission or mechanical ventilation than individuals with the Delta variant.
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