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expert reaction to BA.2 sub-lineage

A comment from Professor Francois Balloux on the Omicron variant sub-lineage, BA.2, which was designated a Variant Under Investigation by the UK Health Security Agency (UKHSA) on Friday.


Prof Francois Balloux, Professor of Computational Systems Biology and Director, UCL Genetics Institute, UCL, said:

“Viruses tend to evolve fairly fast with different strains constantly acquiring mutations over time. SARS-CoV-2 is no exception to this pattern, with each lineage acquiring two mutations a month on average.”

“The accumulation of mutations leads to constant diversification of the viral population in circulation. The Omicron variant which is now dominant globally has been split into three sub-lineages (BA.1, BA.2 and BA.3).”

“Additional Omicron sub-lineages will undoubtedly be described in the future. The previously globally dominant Delta variant D comprised over 200 sub-lineages before it got replaced by Omicron.”

“The BA.2 sub-lineage has been elevated to the rank of Variant under Investigation (VuI) as its frequency has recently increased in some countries including the UK and Denmark, but not in others where it is also present, such as the US.”

“BA.1 and BA.2 are about 20 mutations apart. Interestingly, the two Omicron sub-lineages are sister clades that split from each other several months ago, and are not derived from each other. Both carry a roughly comparable mutations relative to the ancestral SARS-CoV-2 strain.”

“Only a minority of the ~20 mutations distinguishing BA.1 from BA.2 fall within regions of the genome important for antibody immune recognition. As such, it is anticipated that infection by either sub-lineage should provide robust immunity against the other one, as well as against itself.”

“There is no evidence so far that BA.1 and BA.2 are different in respect of immune escape, virulence or the age profile they preferentially infect. At this stage, BA.1 and BA.2 can be considered as two epidemiologically largely equivalent sub-lineages of Omicron.”

“Based on all the current evidence available, changes in the relative frequency of the BA.1 and BA.2 Omicron sub-lineages do not warrant the imposition of any pandemic restriction or the lifting of existing ones.”



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