Omicron grows 70x faster than Delta in lungs but is less severe: Study

The hyper mutated Omicron Covid-19 variant infects and multiplies 70 times faster than the Delta variant and the original SARS-CoV-2 in human lungs, according to a study.

This may explain the reason why Omicron is transmitting much faster between humans than previous variants, said researchers from the LKS Faculty of Medicine at The University of Hong Kong (HKUMed). The variant is now spread to about 77 countries as per the World Health Organization (WHO).

After successfully isolating the Omicron variant in the lab, the team used lung tissue removed for treatment of the lung, which is normally discarded for investigating virus diseases of the respiratory tract, to compare infection with the original SARS-CoV-2 from 2020, the Delta variant and the recent Omicron variant.

They found that the novel Omicron variant replicates faster than the original SARS-CoV-2 virus and Delta variant in the human bronchus. At 24-hours after infection, the Omicron variant replicated around 70 times higher than the Delta variant and the original SARS-CoV-2 virus.

In contrast, the Omicron variant replicated less efficiently (more than 10 times lower) in the human lung tissue than the original SARS-CoV-2 virus, which may suggest lower severity of disease. The research is currently under peer review for publication.

"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, that is `cytokine storm`," said Dr Michael Chan Chi-wai, Associate Professor at the varsity`s School of Public Health.

"It is also noted that, by infecting many more people, a very infectious virus may cause more 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 the Omicron variant is likely to be very significant," he added.