The Chief Medical Officer Dr Tony Holohan has said international travel could be riskier in the weeks before Christmas than it is now.
Final arrangements are being made to roll out the EU's traffic light system here on Sunday, which will see countries branded green, red or orange.
Under the plan, regions will be designated green if they have a 14-day rate below 25 and a positivity rate below 4%.
Regions with a 14-day below 50 will be designated orange provided their positivity rate is above 4% - however, they can have a 14-day rate as high as 150 if their positivity rate is less than 4%.
All other regions will be designated red.
But the possibility of families reuniting at airports for Christmas has been hit with fresh doubt.
Dr Holohan has told the Oireachtas Joint Committee on Transport and Communications that international travel is simply unsafe, and the risk is likely to increase in the weeks before Christmas.
"The level of disease transmission in this country is improving at a point when the vast majority of countries in Europe are disimproving".
'Not many 'green' countries'
He said they are currently "working through" how best to adopt testing arrangements for orange and red countries.
"It'll also then be a function of where other countries are in terms of the disease - if it's in a European context, what colour they are at a point in time.
"If I was to guess I'd say there probably won't be many countries on 'green' by the time we're talking about Christmas flights.
"I think it'll be difficult for very many countries to be anything other than 'red' at that point in time".
The traffic light system will see different rules apply, depending on what colour country passengers are arriving from.
However it is likely to include testing passengers and asking them to restrict their movements for a period of time.
Dr Holohan said it is impossible to say now if public health officials will be able to change their stance on non-essential travel in time for Christmas.
"We can only make that assessment at a point in time and make our advice available at that point in time.
"I understand completely the sensitivity that there will be for families, and for people who are thinking about these kind of arrangements, wishing to come back together".
"I'm not ruling anything out, I know where we are at the moment and what progress has to be made."
"Our advice will be in two directions: we'll have advice obviously to Government at a point in time based on our assessment of the disease - both in this country, internationally - and the risks that might arise in terms of travel".
Dr Holohan said this work is ongoing at the moment.
On implementing the traffic light system, he said: "This is happening right at the moment.
"There's an ongoing process with colleagues across Government departments, led by the Department of the Taoiseach, to consider all the practical arrangements that must be in place to enable the implementation of the Government's decision.
"Our advice has been reflected into that process".
Irish alignment
While travel expert Eoghan Corry has previously said a number of stumbling blocks have hampered the new system.
"It's not quite clear how aligned we are.
"Hildegarde Naughton said last week before the Oireachtas Committee that it looks like we are going to start treating amber countries or orange countries as the same as red countries.
"It's also not clear [if] we're going to adopt it by region - that would be important, for instance, for the likes of the Canary Islands being stripped away from mainland Spain.
"It's also not clear if we're taking the metric of 4% positives, which is one of the metrics that went before the commission.
"It does look like we have said we're aligning with the EU policy, and only taking a little bit of it.
"This is complicated a bit by the fact that the EU policy that went before the ministers, and went into that room, isn't the same as came out.
"What went to the Council of Ministers from the Secretariat was that states would give two weeks notice of a change in policy.
"When it came back out from the room with the ministers, it said 24 hours.
"That means nobody can plan a trip and no airline can plan a schedule.
"It also gives a huge degree of opting out to the member states."
Additional reporting: Kacey O'Riordan
