The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant of concern has spread rapidly since its emergence in late 2021. Presently, an Omicron subvariant known as BA.2, first identified in late 2021, has made headlines due to its rapid spread.
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Omicron mutated into sister sublineage BA.2
While Omicron has approximately 60 mutations, it is thought that its sister lineage may have 85 mutations. The World Health Organization (WHO) stated over the weekend that this lineage differs from the original Omicron strain by several mutations, including those of the spike protein, the SARS-CoV-2 protein that mediates host cell entry. This variant has also been termed the “stealth variant” due to a mutation that renders it ‘invisible’ as Omicron to PCR testing.
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.” Professor Francois Balloux, director of the UCL Genetics Institute
BA.2 has spread to over 40 countries, including the US, UK, India, Australia, and Norway. In the latter, it currently accounts for half of Omicron cases. It is currently unknown why BA.2 has dominated so quickly in Norway; however, enhanced immune escape or transmissibility has been suggested.
What this means for public health
Current reports liken the symptoms of the new lineage to that of the original strain of Omicron: sore throat, headaches, nausea, etc. It is believed that there are no differences in disease severity, with some even suggesting the symptoms are milder.
Scientists currently understand that previous Omicron infection confers protection against BA.2 and expect the already developed vaccines to be effective against the Omicron subvariant. Nonetheless, the WHO has made recommendations that understanding the immune escape characteristics of BA.2 is of great priority.
With reports of yet another Omicron subvariant, BA.3, it is of ever-increasing importance to track the emergence of new SARS-CoV-2 strains and understand their implications on public health.