Just three weeks after its notification to the World Health Organisation, omicron has spread around the world and is now well-established in the UK.
Dair wythnos yn unig ar ôl iddo ddod i sylw Sefydliad Iechyd y Byd, mae omicron wedi lledaenu o gwmpas y byd, ac mae bellach wedi hen gyrraedd y DU.