Ireland's top public health official has reiterated his warning that a wave of Omicron cases is on the way within weeks.
Dr Tony Holohan said the new variant is spreading at a faster rate than any other previous strain as he cautioned the public ahead of Christmas.
Around 66% of all infections can now be attributed to Omicron, with the incidence "dramatically increasing" among 16 to 34 years olds.
The Chief Medical Officer acknowledged that young adults have made "exceptional sacrifices" during the pandemic but urged this younger cohort to reduce their contacts over the festive season.
He is also appealing for people to only meet those this week with whom they plan to spend Christmas Day.
Dr Holohan said NPHET want to give young people "practical" things to do to minimise the risk of catching or spreading Covid this week, including cutting contacts and staying away from crowded settings.
"These are not messages we want to be giving at Christmas time...it gives me no pleasure to be giving people this advice at this time of year," he told RTE's Today with Claire Byrne programme.
"We're facing a very significant surge in infection, we can already see the very rapidly rising rate between the ages of 16 and 34.
"The increase in incidence we're seeing is not confined to those age groups but it is dramatically increasing in those age groups at this point in time.
"That's consistent with what we're seeing in other European countries like the UK, Denmark, Norway and the Netherlands.
"It's also consistent with what we've seen in previous waves of infection in this country, it often spreads among young people first and that's not pointing the finger in a particular direction, that's simply making the epidemiological point that that's how the infection spreads and gets transmitted so easily.
"But this particular variant has a growth advantage, we think, made up of some inherent transmissibility advantage, number one, and its ability to escape some of the protection that's afforded by vaccination or by previously having had an infection.
"As a result, it's spreading much more rapidly than any variant we've ever seen before."
Dr Holohan added that one in six young people have not been vaccinated, while one million people over the age of 40 have not yet come forward for their booster dose.
He said further data is needed on the severity of Omicron when it comes to its ability to cause severe illness.
However, he stated: "Vaccines really work, particularly when boosted, in preventing infection from becoming a severe infection and we expect that to be the case with Omicron."
Meanwhile, an Infectious Diseases Consultant at St James's Hospital in Dublin has warned that Omicron is "spreading like wildfire".
Dr Cliona Ni Cheallaigh said the next week or two will tell a lot in terms of potential hospitalisations as a result of the latest variant.
“What is more important is how many of the cases become seriously unwell and require hospital care or have their lives threatened by Covid,” she told Newstalk.
“I think that will determine what level of restrictions are needed in the following weeks and we just don’t know that yet.
“It definitely spreads like wildfire; I think we can see that very clearly and if that results in people becoming seriously unwell, then we will need to think about further restrictions.”
Have your say on the Christmas restrictions below, or click here.
