Omicron infects 70 times faster, but less severe

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Chinese researchers were able to determine in a study that Omicron attacks the bronchial tubes more than the lungs. Progression is milder.

A study led by researchers at the University of Hong Kong’s LKS Faculty of Medicine (HKUMed) provides the first information on how the new Omicron infects people’s airways. The researchers found that Omicron infects and replicates 70 times faster than the Delta variant and the original Wuhan variant. This could explain why Omicron may be transmitted between people faster than earlier variants. Their study also showed that Omicron infection in the lungs is significantly lower than the original SARS-CoV-2, which could be an indicator of less severity of the disease. This is because the variant mainly infects the bronchi. The study is currently in peer review for publication.

For the study, virologist Michael Chan Chi-wai and his colleagues took tissue from human bronchi – the two large tubes in the airways that bring air into the lungs. The researchers infected the tissue with live, replicating particles of the SARS-CoV-2 virus. They used three versions of the virus: delta, omicron and the original version.

Then the researchers studied how quickly each variant spread through the respiratory tissue. Within 24 hours, Omicron had infected tissues 70 times more than was observed with the Delta variant.

Chan and his colleagues also conducted the experiments with lung tissue. Interestingly, Omicron was less efficient at infecting cells in this tissue than Delta or the original version of the virus.

“It is important to note that the severity of disease in humans is determined not only by virus replication, but also by the host immune response to infection, which can lead to a dysregulation of the innate immune system, a ‘cytokine storm,'” Dr. Chan said.

“It also suggests that a very infectious virus can lead to more severe disease and death by infecting many more people, even though the virus itself may be less disease-causing. Therefore, together with our recent studies showing that the Omicron variant can partially escape immunity through vaccines and past infections, the overall threat of the Omikron variant is likely very significant.”