The Chief Medical Officer has advised people to limit their social contacts this week to those with whom they will spend Christmas Day.
Dr Tony Holohan urged: "This week, try and only meet with the people with whom you will spend Christmas Day. Keep your contacts as low as possible in order to protect those around you."
It comes as the Department of Health confirmed 5,279 new cases of Covid-19.
This morning there were 443 people in hospital who had tested positive for the virus, down 24 since yesterday. Of these 102 are in ICU, a reduction of two.
Tonight, the number of Covid patients in hospital had reduced to 396 in total.
The Omicron variant now accounts for "about two thirds" of confirmed cases of Covid-19 in Ireland, according to Dr Holohan.
The Chief Medical Officer warned: "Public health teams are reporting a higher level of infection among household close contacts as a result of Omicron infection.
"If there is one positive test, whether from a PCR or an antigen test, within a group such as a household then there is a significant chance that others are already infected, even if not yet testing positive.
"If one person from a household tests positive prior to an event or gathering, then none should attend."
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Dr Holohan added: "As we continue to see incidence rising in our young adult population, I would urge all parents, guardians and extended friends and family to support the young people in your lives to reduce their contacts.
"I know that this is not an easy task for any of us and it can feel very unfair that we continue to ask so much of our young people, particularly at this special time of year.
"This group have made significant sacrifices in order to protect loved ones and I would like to thank them for that.
"It is important now that we continue to encourage and support each other to make sacrifices, take responsible actions and continue to follow the public health advice."
The Chief Medical Officer continued: "As we roll out the booster programme, it is important to remember that approximately one in six young adults are yet to come forward for vaccination or are not fully vaccinated.
"Vaccination offers very good protection against severe illness, so it is important that everyone who is eligible for a vaccine comes forward for one.
"If you display any symptoms of Covid-19 then you must self-isolate straight away and arrange a test.
"This is the single most important piece of basic public health advice. Do not meet up with others and put them at risk. Do not rely on a negative antigen test as a basis for not isolating."
Earlier, the Minister for Health announced that the current wait period for a vaccine following recovery from Covid-19 is to be shortened from six to three months for those who are fully vaccinated.
Stephen Donnelly said: "Decreasing the interval for booster doses in those who have had a breakthrough infection is an important step given Ireland's current epidemiological situation."
Some members of the public now have the option of scheduling their own appointment for a booster vaccine at a select number of vaccination centres.
The self-scheduler is available for anyone aged 40 and older, or for people aged 30 and over that are either pregnant, a healthcare worker, have an underlying condition, or are living in a nursing home or a long-term healthcare facility.
In Northern Ireland, a further 2,096 new infections have been reported, along with three further deaths.
It comes as DUP leader Jeffrey Donaldson has said he has tested positive for Covid-19.
Also today, the Government announced enhanced business support schemes for the hospitality and arts sectors hit by the latest restrictions.
Compliance with self-isolation 'an issue'
Separately, a professor of behavioural research at the ESRI has said that compliance with self-isolation has been an issue since the start of the pandemic and is not a new development.
Professor Pete Lunn said that since the early days of the pandemic there have been people who have been symptomatic, but believe the symptoms are mild and that they do not have Covid.
Research shows these people follow public health guidance and yet fail to self-isolate, he told RTE's Today with Claire Byrne.
Prof Lunn said that young people have been disproportionately affected by the pandemic and should not be blamed for the spread of the disease.
Younger adults have not yet got the booster vaccine and this is a reason many are getting infected, not just because of their behaviour, he added.
He said that younger people are more visible when socialising and "the idea that young adults are the ones taking all the risks is not right".
Prof Lunn said that young people are feeling substantial effects of the pandemic in terms of loneliness and the impact on mental health.
They "are making the largest sacrifices", he said, as the downsides for younger people impact those who are looking for relationships, trying to expand their horizons and trying to get new friendships.
