The Taoiseach has indicated that public health restrictions could stretch out to the summer due to concerns over new variants of Covid-19.
He also said the reopening of schools may have to be phased in, with special schools the first to allow children back in.
In a lengthy and sobering interview on RTÉ radio, Micheál Martin also said he had spoken last night with UK Prime Minister Boris Johnson about the new UK variant and the indications that it may lead to a 30% increase in mortality compared to the strain of the coronavirus that first hit this country 10 months ago.
The Taoiseach also said any idea of a two-island approach to quarantine was at an "embryonic" stage and said he did not feel an all-island approach was "practical or doable".
Mr Martin also reflected on the spiralling number of positive Covid-19 cases since Christmas and admitted that lessons needed to be learned, while also saying that the decision to ease restrictions ahead of the festive period had been based on multiple factors and without a full sense of the extent or potential dangers of new variants of the virus.
The overall sense from the Taoiseach was of caution, even as vaccine rollout takes place around Europe and Ireland, hampered by delivery target issues over the AstraZeneca vaccine.
He said he was "very worried" about the emergence of variants, saying they had the ability to undermine the effect of vaccine rollout, which he said was a "race against time". He also said he was concerned about the potential of new variants to undermine the vaccine efficacy.
"By the summer I think we will be in a changed environment," the Taoiseach said.
"I am sounding here this morning [a note of] caution and a conservative approach now because of how the virus is evolving."
The government has already signaled that current level 5 restrictions will remain in place well into February before being reviewed ahead of March, but Mr Martin said the impact of rising numbers since Christmas would impact on plans to reopen society into the future.
"I don't think anyone saw the level of 6,000 [cases] a day," he said.
"There was an expectation that we would be going back into three-week lockdown in January."
He said that was based on estimates of a couple of hundreds of cases a day, and that "a sense of human behavioural analysis" in easing restrictions over Christmas.
"We have got to learn from it," he said.
As for restrictions on those entering the country, he said: "We are looking at other quarantining options."
Those would impact on people coming from countries such as South Africa and Brazil, where variants have emerged, he said.
"The object of this is to deter people, to make it so Goddamn awkward that people won't be bothered travelling," he said, adding that many of those coming into the country were returning holidaymakers. He urged people not to travel overseas in the coming months.
The Taoiseach also said he spoke with Prime Minister Johnson last night, primarily about the UK variant of the virus.
"He is worried about the variant, there is something going on out there, as a layperson would say," Mr Martin said.
He referred to "whole wards getting infected" and observations from the HSE that the spread now was different from the first months of the pandemic.
He said any thoughts on a two-island approach to quarantining was "embryonic" and said of a possible an all-island approach: "I don't think it's practical or doable.
"It's just not that simple, there are particular issues."
He also accepted that the u-turn on re-opening schools for children with special education needs was "a failure all round".
"There is a shared determination to do something for families with special needs in particular," he said, adding that while he did not want to give a timeline he hoped it could happen "in the coming weeks".
"If it comes sooner, fine," he said. "It is our priority".
However, he dampened any expectations that all schools will reopen soon.
"We are going to have to look at it differently now in terms of reopening schools, not the one big bang approach because of the transmissibility and that, I think we have to get the numbers down."