The country is doing substantially better in terms of Covid cases, numbers in hospital and deaths than the National Public Health Emergency Team's optimistic models, Tánaiste Leo Varadkar told the Fine Gael Party tonight.

For this reason, he said he was sceptical that imposing new restrictions on people's freedoms, family life and businesses would be warranted at this time.

But he added there was a concern that things have stabilised at a high level and if anything went wrong in the run up to Christmas, it would go wrong from a very high base.

He said there was a genuine cause for concern with people socialising more at Christmas and the Government would carefully listen to NPHET's advice on the matter tomorrow before making any decisions.

Earlier, Chief Medical Officer Dr Tony Holohan said that while there are encouraging signs that infection rates of Covid-19 have stabilised, this is at a very high level with well over 1,300 cases per 100,000 population on a 14-day incidence rate.

It comes as the Department of Health confirmed 3,793 new cases of Covid-19.

There are 578 people in hospital who have tested positive for the virus, down one since yesterday. Of these 117 are in ICU, five fewer than yesterday.

There has been a total of 5,707 deaths related to Covid-19 notified in Ireland. This includes 55 deaths newly notified in the past week.

In Northern Ireland, 1,992 new coronavirus infections and four deaths were reported today. There are 332 Covid-positive patients in hospital, of whom 30 are in intensive care.

Speaking on RTÉ's Six One News, Dr Holohan said the more progress that can be made in reducing levels of transmission among younger children and on rolling out booster vaccines, the greater protection there will be in advance of the Christmas period.

He said the reduction of transmission in population groups who have received booster vaccines have been particularly impressive, but there has been a slowing of the disease in most adult age groups.

Dr Holohan said it is not yet known if the new Omicron strain will be more transmissible, if there are implications for how well the vaccines will work and if it will be as severe as the Delta variant.

These unknowns, coupled with the risk of a very high level of infection in a context where contacts might increase across the population, suggests that "a cautious approach" is needed.

Dr Holohan said that Christmas is an important time for socialisation and a time of year when families come together and there is a lot more mixing between younger and older members of the population.

He said we know that infection levels are highest in younger children because this group is not vaccinated. The concern would be for younger people mixing with older people who are not yet boosted, he added.

Meanwhile, in relation to the first case of Omicron detected here, Dr Holohan said: "Today's notification of a confirmed case of the SARS-CoV-2 Variant B.1.1.529 (Omicron) should not change how we are responding to the public health measures that are already in place.

"The best mitigation we have against transmission of this virus, regardless of the variant, are the public health measures that we are so familiar with and more importantly, that we know will work."

The number of outbreaks of Covid-19 increased last week by 29 to 151, latest figures show.

There were 47 outbreaks in hospitals while outbreaks in schools rose by 21 to 45.

The schools figure is in the context of routine close contact tracing having ceased in primary schools in late September for asymptomatic close contacts among children aged 12 years and younger.

There were 30 outbreaks in residential institutions and 12 in nursing homes last week. There were no outbreaks recorded in pubs or hotels in the same period.

The Health Protection Surveillance Centre (HPSC) said the number of outbreaks in some settings may be an underestimate, due to a public focus on key settings at present.

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An outbreak is two or more linked cases. The figures are from the HPSC and cover the week to last Saturday.

Earlier today, an assistant professor of virology at University College Dublin said antigen testing on passengers coming into Ireland will not reduce the spread of the Omicron variant of Covid-19 and is just "window dressing".

Dr Gerald Barry said there should be a bigger emphasis on controlling the spread of the disease within the country, rather than focusing on border controls.

From Friday, people arriving at Irish ports and airports will need a negative Covid-19 test and can either have a professional antigen test taken a maximum of 48 hours prior to arrival, or a PCR test taken up to 72 hours earlier.

The requirement for a negative test applies to all arrivals, including those from Britain.

Speaking on RTÉ's Morning Ireland, Dr Barry said it is necessary to dramatically ramp up the testing and tracing system to detect new cases and rapidly clamp down on them.

He said the intention behind antigen testing before flights to reduce variants is correct, but the manner in which it is being done "will not achieve that aim".

It is "completely pointless" to carry out antigen testing 48 hours ahead of travel and he added that a number of tests would be needed before and after a journey, as a once-off test does nothing to properly identify the virus.

The evidence for using PCR tests is "stronger" Dr Barry said, but a 72 hour window is "probably too long".

"It also leaves the window of getting infected on the flight, which we know evidence points to is possible as well," he said.

Ireland is massively under testing and under sequencing cases, Dr Barry said, and there may be many more Omicron cases here that have not been detected.

"We are only sequencing around 10% of our cases, so there is probably lots of cases in the country," he said.

Meanwhile, the President of the Infectious Disease Society of Ireland said antigen tests for international travel need to be of high quality and repeated twice in the days after travel to maximise the benefits of the measure.

Speaking on RTÉ's Today with Claire Byrne programme, Professor Sam McConkey said it is "a step in the right direction" and will slow down the entry of the Omicron variant into Ireland, but that people need to "do more and make sure the tests are high quality".

He said contact tracing for young people is "very wise" and the introduction of face masks for primary school children was hopefully a temporary measure.