Omicron appears to multiply 70 times faster than ancestral versions of the Sars-CoV-2 in a part of the human body known as the bronchus but less efficiently in the lungs, the University of Hong Kong (HKUMed) said on Wednesday, citing work by its researchers that could explain why the new variant of concern (VOC) has an unprecedented transmission advantage.
The new research, currently under peer review, was based on a lab study in which the scientists examined the way an isolated Omicron variant infected tissues taken from different parts of the respiratory tract, and compared it with similar experiments using other versions of the virus.
Omicron replicated in the bronchus 70 times faster than the Delta and the ancestral variant, which may explain why it “transmits faster between humans”, HKUMed said in a statement. It also found that Omicron’s replication in the lungs was significantly less efficient – “more than 10 times lower” – which could explain the reduced disease severity being reported from some parts of the world, it added.
The bronchus is a passageway in the lower respiratory tract that leads air into the lungs.
One of the scientists involved cautioned against drawing premature conclusions about the variant being milder. ‘It is important to note that the severity of disease in humans is not determined only by virus replication but also by the host immune response to the infection, which may lead to dysregulation of the innate immune system, or “cytokine storm”,’ said Dr Michael Chan Chi-wai, associate professor of School of Public Health.
He added that by being able to infect many more people, Omicron can lead to more cases of severe disease and death “even though the virus itself may be less pathogenic”.
“Therefore, taken together with our recent studies showing that the Omicron variant can partially escape immunity from vaccines and past infection, the overall threat from Omicron variant is likely to be very significant.”
The findings mirrored another study that found a significant difference in how the infection occurs at the cellular level, where Omicron is substantially more capable than its ancestors.
Omicron (the researchers used an engineered version of the virus) was able to infect target cells containing what is known as the ACE-2 receptor substantially better than variants like Beta and Delta, found the second study, which was led by researchers from the Ragon Institute of MGH, MIT and Harvard.
The newest VOC’s infectivity was two-fold higher than Delta’s and fourfold higher than the variant first seen in Wuhan.