The Chief Medical Officer has warned of a "high level of disease in young people" as Covid cases continue to remain high in Ireland.
Dr Tony Holohan warned that "the level of disease and positivity rate amongst young adults has increased sharply in the last week", with one age cohort particularly affected.
It comes as a further 4,799 cases of coronavirus were reported on Monday, while a range of new restrictions impacting hospitality, events and close contacts also came into effect.
The CMO said that one in four people in the 16 to 34-year-old age group that are going for a PCR test have received a “detected” result.
This represents "one of the highest rates since the beginning of the pandemic", he warned.
“This high level of disease in young people represents a high risk to those they come into contact with who have yet to be vaccinated or receive their booster," Dr Holohan said.
"Therefore, if you have not yet received your booster you are best to avoid unnecessary contact with people outside your household."
With just four days until Christmas, the CMO also appealed to people to make an "exceptional sacrifice" when it comes to socialising over the festive season.
He said: “Christmas week is an important time for many of us. However, it is also a time that presents unique opportunities for Covid to spread because of the possible extent of inter-household and inter-generational mixing.
"Each of us can take actions this week to protect ourselves and our loved ones, even if this means rethinking plans for the Christmas period, especially if you are not yet boosted or vaccinated.
“As difficult as it may seem, limiting as much as possible your Christmas to small numbers and very close family will protect them.
"This is an exceptional sacrifice to ask after the very difficult year all of us have had, so please remember that it may be the decision that protects yourself or a loved one from the severe impacts of Covid-19."
Dr Holohan added that new research from Amarach shows that "only half of people with symptoms are isolating".
"This is the single most important piece of basic public health advice - it is vital that you isolate as soon as you experience any symptoms of Covid-19 and arrange a PCR test," he said.
"Do not meet up with others and put them at risk of Covid-19 or another respiratory infection. Do not rely on a negative antigen test as a basis for not isolating."
Earlier on Monday, the top public health doctor expressed his concern about the Omicron variant as he urged people to adopt personal responsibility when it comes to their activities over the festive season.
He said Ireland is "potentially at risk from a major surge of the virus" that is now being felt in countries across Europe including Norway, Denmark, the Netherlands and the UK.
"The measures that have been taken are intended to substantially cut the quantum of social contact across society," he said.
"Government has now made these decisions and mandated them and you as an individual can start to take measures to cut your own social contact.
"Over the course of the coming days, think about the things you absolutely have to do, the things you may not need to do.
"It's a difficult message at this time of year, I completely understand at Christmas time."
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