A New Year lockdown may be inevitable as socialising looks set to trigger a January surge in Covid-19 cases.
Chief Medical Officer Dr Tony Holohan issued his strongest warning yet about another potential spike in cases after Christmas and New Year celebrations, which could cause a return to tougher restrictions.
He said the chances of a significant January escalation in infections is "more likely than unlikely".
Dr Holohan also pointed to "anecdotal" reports that, only days after reopening, there are overcrowded restaurants.
He appealed to people to "walk away" from such risky situations.
"If we are asking ourselves honestly how likely it is that we can avert a significant surge of infection in January, it's probably less likely than more likely," he said.
Experts told the National Public Health Emergency Team (Nphet) that virus case numbers could, at a "conservative level", reach 300 to 600 a day by early next month.
However, Dr Holohan, in a letter to the Government last week, indicated the more probable scenario is 300 to 450 a day by New Year's Day and 800 to 1,200 by the second week of next month.
Asked last night about the prospect of a third lockdown, he said: "We don't want to be in the position where we have to make an assessment and recommend more severe restrictions."
However, he added: "If we have to do that, it is what we will do."
Controlling the spread is reliant on individuals following the restrictive measures that are in place, Dr Holohan said, along with an efficient HSE response to quickly leap on outbreaks at an early stage and control them, stopping the virus spreading into the wider community.
However, there appears to be some concern about the strength of the HSE response if virus cases shoot up again.
The Government was also warned about the risks posed by Christmas homecomings by family from abroad as well as by people flying out on sun and ski breaks from Ireland over the next few weeks.
They could potentially bring the virus back with them and help to rapidly undermine the lockdown progress that was so hard won.
Dr Holohan was speaking as 242 more cases of the virus were reported yesterday, with no additional deaths.
Research carried out on behalf of the Department of Health highlights how people are now less concerned about the pandemic.
At the same time, there is a slight increase in the five-day moving average of the virus and a 13pc rise in the seven-day incidence rate.
Seventy-eight per cent of people say they are staying at home rather than going out compared with 90pc in April.
Overall, there is considerably less worry about the pandemic, which is leading to a rise in contacts and a stronger chance of passing on the virus.
There has been a fall in the numbers of people believing the worst is yet to come, and more are convinced we have now seen the grimmest days of the pandemic.
Asked about the possible arrival of a Covid-19 vaccine, Dr Holohan said the European Medicines Agency, which will decide if it will be given the green light for Ireland and other European countries, will not meet until the end of this month.
Our high-level task force charged with planning its roll-out will report by Friday, he added.