Why are there so many types of Omicron? A mutation is a common concept in viruses. However, according to a report by The Conversation, the vast majority of mutations have little to no effect on the ability of the virus to transmit from one person to another or to cause severe disease.
When a virus accumulates a substantial number of mutations, it’s considered a different lineage (somewhat like a different branch on a family tree).
But a viral lineage is not labelled a variant until it has accumulated several unique mutations known to enhance the ability of the virus to transmit and/or cause more severe disease.
This was the case for the BA lineage (sometimes known as B.1.1.529) the World Health Organization labelled Omicron. Omicron has spread rapidly, representing almost all current cases with genomes sequenced globally.