The Chief Medical Officer has said that people "can take measures today" to ensure the "safest possible interaction" with family and friends over Christmas.
Dr Tony Holohan called on the population to "risk assess the environments you plan to be in over the next two weeks".
His comments come as the Department of Health confirmed 4,115 new cases of Covid-19.
There are 511 people in hospital who have tested positive for the virus, down 19 since yesterday. Of these 110 are in intensive care, a reduction of five.
Dr Holohan said: "We are in a very uncertain and unstable position due to the high incidence of Covid-19 in Ireland driven by the highly transmissible Delta variant.
"This is a matter of very significant concern as we wait for more evidence relating to the Omicron variant and the impact it may have to emerge.
"At the moment, based on the evidence available to us, we believe the public health measures we are so familiar with will work to slow and stop the transmission of the Omicron variant, as well as the Delta variant."
He added: "Early indications suggest that a booster dose of Covid-19 vaccine will offer good protection against infection from Delta and Omicron.
"If you are eligible for a booster dose, then please take the opportunity to receive your vaccine as soon as it is available to you."
Today, Taoiseach Micheál Martin was spotted queuing for his booster jab at City Hall in Cork city.
The Fianna Fáil leader received the two-dose AstraZeneca vaccine earlier this year.
Speaking to reporters afterwards, Mr Martin said he was "concerned" about the Omicron variant and the impact it could have after Christmas or even before that.
He said that the evidence so far is that Omicron doubles in transmission faster than the Delta variant, but more details are needed.
Mr Martin said the evidence so far seems to suggest that the vaccines work against the latest variant in terms of providing protection against serious illness.
"The big issue is to what degree is it severe and does it create serious illness or not and does it escape the vaccine," he said.
The Department of Health said yesterday that six cases of Omicron have so far been detected in Ireland.
The latest variant will be on the agenda for European Council members at their meeting next week, the Taoiseach said, "assessing the prevalence and the coordinated measures that we might be able to take".
Asked about the latest restrictions and the possibility of more to come, Mr Martin added: "One can never rule out anything in relation to Covid-19 because there are many twists and turns.
"But what I think is important is that we adhere to the guidelines that are in place and also the restrictions that have been brought into play."
Holohan advice for festive season
Issuing his advice for the festive season, Dr Holohan said: "We are all aware that this day two weeks is Christmas Eve, a time of year when we all look forward to coming together with friends and family.
"You can take measures today and in the next few days that will ensure the safest possible interaction with your loved ones over Christmas.
"Risk assess the environments you plan to be in over the next two weeks - consider if they offer the opportunity to protect yourself with each layer of the public health advice and if you can:
- Avoid crowds and reduce your contacts
- Wear a mask including in crowded outdoor environments
- Keep your distance if you feel unsafe feel empowered to leave
- Open windows and avoid poorly ventilated indoor spaces
- Clean your hands regularly."
Meanwhile, all passengers arriving into Ireland from Britain are being advised to carry out an antigen test every day for five days after arrival.
Dr Holohan said doing this would greatly increase the chances of picking up cases of the Omicron variant imported into Ireland.
Around 891,500 people in England - the equivalent of around one in 60 people - had Covid-19 in the week to 1 December, according to official estimates.
The disease affected around one in 50 people in Wales and one in 80 people in Scotland during that time.
It is estimated that 39,300 people had the virus in Northern Ireland in the week ending 1 December, equating to around one in 45 people.
A further 1,806 positive Covid-19 cases were reported by Stormont's Department of Health today, along with two further deaths.
Additional reporting Conor Kane