Initial data shows the risk of being admitted to hospital after being infected with Omicron, is between 50 and 70% lower than for Delta.
132 people with the variant have been admitted in England - 40% of those were in London - and the smallest group was of people who'd received a booster vaccine.
Latest HPSC data for Ireland - up to Saturday showed just five patients with Omicron have been hospitalised here.
But the UK Health Security Agency says protection from a third dose starts to wane more rapidly against Omicron - within about 10 weeks.
