Ireland could see up to 1,200 cases a day of coronavirus after Christmas, a public health expert advising the Government has warned.
The health system is braced for a significant rise in the reproductive rate of the virus unless people keep discretionary meetings to a minimum after the country exited level 5 restrictions this week.
Public health experts said the level of infection was "static" but with a persistently high incidence in older people.
Chief medical officer, Dr Tony Holohan, said the renewed lockdown would produce a low of around 250 cases a day.
"That underscores the importance of each one of us recognising what a potentially fragile situation we are in but that will not inevitably lead to some of the potential R number increases that we have modelled."
He warned if large numbers over the next three weeks adopted "discretionary" socialising, such as going to restaurants, it could leave the health system in a "precarious" situation.
"If people can limit the extent that they have social engagements that are discretionary and avoid those, particularly in the weeks running into Christmas, we have a chance we can maintain some control in terms of transmission levels and we will not find ourselves as a country experiencing rapid growth of infection."
He said he did not want to have to recommend further restrictions in future.
Professor Philip Nolan, modelling the spread of the virus for the Government, said the reproductive rate of coronavirus was 0.8-1 at present.
He said: "The more contacts, the higher the R number will go, the higher the number of cases we will be seeing in January."
Professor Nolan said small increases in the R number to 1.6 could produce between 800 and 1,200 cases a day.
Dr Holohan said: "It is not inevitable.
"It is still within our grasp as a country to take the kind of measures that can help protect against that reality."
He said the modelling was not scaremongering and these were not predictions.
"These are plausible.
"We are not applying an R number of four to the numbers, we are applying very small differences."
Earlier, the Tanaiste said people buying tickets for concerts next summer should be aware they will not be entitled to refunds if the events are rescheduled.
Leo Varadkar said there was "no guarantee" such events would go ahead and that it may be "some time yet" before mass gatherings are allowed.
The music festival Longitude has announced its return in July 2021, an event that typically attracts 40,000 people.
Mr Varadkar said: "There are now tickets on sale for some major events that we all hope will go ahead next summer.
"The advice I would say is that there is no guarantee that those events will go ahead.
"It might be some time yet before we can attend matches, concerts and mass gatherings.
"I hope it is possible in the summer, but that's far from sure at this point."