The Tánaiste Leo Varadkar says the Government hoped the country would get to January without another lockdown.
It comes as Ireland is going back into a level five lockdown from midnight on December 24th until January 12th.
However a number of changes have been implemented to these restrictions, including the opening of non-essential retail.
But they have been asked to defer any January sales events.
Speaking to The Hard Shoulder, Mr Varadkar said there is "always hope" that restrictions could be lifted earlier - but this is unlikely.
"We've seen how this virus can turn rapidly and has turned rapidly in the last week in the wrong way".
"The restrictions that we're introducing are being phased in between now and New Year's - you would expect to see the effects not until the trees come down around the 7th or 8th of January."
He said the roll-out of the vaccine from December 30th should change the game.
"I think probably where we are now, for the first part of next year, is with these restrictions in place.
"But trying to get a sufficient number of people vaccinated so that it changes the calculus.
"By vaccinating people in nursing homes, healthcare workers, that'll change the case fatality rate, it'll change a lot of the way we look at this disease".
He said the Government wanted to avoid "constant on-off lockdown", but plans change.
"We really thought this time we would get to the middle of January, in line with projections, before we had to tighten restrictions."
But he said that the virus "continually makes a fool of our plans".
"Having said all that, though, let's not forget that we have done well relative to other European countries.
"We've had among the lowest number of cases, among the lowest number of deaths in the past six months, no excess deaths this winter so far.
"No more people died this winter than the average of the last five winters, and that's an extraordinary achievement by our society".
He explained: "If we didn't do the things we're doing as a society we would have excess deaths".
Northern Ireland 'a chink in our armour'
A travel ban from the UK has also been extended until the end of the year.
It comes as cases of a new coronavirus strain have been spreading rapidly in Britain.
The mutation - known as VUI-202012/01 - is said to be up to 70% more infectious than the original strain because it has a much bigger viral load.
However there are no travel restrictions in place between Britain and Northern Ireland - with concerns people can then take trains and buses from Belfast to Dublin and other places.
On this, Mr Varadkar said he believes the new strain is here.
"We don't have laboratory confirmation of that, but we are operating on the basis that it is here.
"Anything that was in England in September is very likely to be in Ireland now".
But he said the Government's plans have been hampered by the open border with Northern Ireland.
"Northern Ireland is definitely a chink in our armour - it's been an issue from the very start.
"But that's the reality of how it is, we've the Good Friday Agreement.
"Northern Ireland is - whether we like it or not - it is an autonomous part of the United Kingdom, it makes its own decisions and we have to respect that".