The Omicron variant multiplies 70 times faster than Delta in human airways, according to researchers.
A new study in Hong Kong provides the first information on how Omicron infects people, and it also suggests it replicates less well in human lung tissue compared with the original strain of the virus.
This could indicate a lower severity of disease, but the experts warned the ‘overall threat is likely to be very significant’.
Dr. Michael Chan Chi-wai said 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’.
The associate professor, from the University of Hong Kong (HKUMed), added: ‘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 Omicron variant is likely to be very significant.’
After successfully isolating the Omicron variant, they began investigating the new mutation with some lung tissue.
They found Omicron ‘replicates faster than the original virus and Delta variant in the human bronchus’.
After 24 hours from infection, the Omicron variant ‘replicated around 70 times higher than the Delta variant and the original virus’, the researchers said.
They added: ‘In contrast, the Omicron variant replicated less efficiently (more than 10 times lower) in the human lung tissue than the original virus, which may suggest lower severity of disease.’
The research is currently under peer review for publication, the university said.
Reacting to the study, Dr. David Strain, from the University of Exeter, said: ‘The 70-fold increase in replication is of concern which does account for the increased transmissibility of the virus.
‘There is a lack of clarity, however, as to how this 10-fold reduction in lung infectivity in this lab-based study will translate in patients.
‘At first glance, it looks good news, however, if the virus can replicate 70 times quicker, but infects 10 times slower, that still results in a seven-fold increased risk of disease (70 times more virus, even with a 10-fold reduction in ability to enter the cells will cause the virus to overwhelm the cells).’