The Chief Medical Officer has said the use of antigen tests for five days post-arrival for travellers from Britain will greatly increase the chances of picking up cases of the Omicron variant imported into Ireland.

The Government issued the advice last night after it received an updated public health assessment of the variant.

Speaking on RTÉ's News at One, Dr Tony Holohan said all early evidence is that booster doses of vaccine will help to offset the severe effects of the variant, and urged people to get vaccinated and receive their boosters.

He said there is a significant challenge in the UK, in particular in Scotland and England, where there is now widespread community transmission of the Omicron variant.

Dr Holohan said the guidance is that people should exercise a high level of caution around travel as it is a high-risk activity and they need to be aware of the risks when making decisions.

He said that a traveller who arrives into Ireland and develops symptoms of Covid-19 needs to immediately self-isolate and do a PCR test.

All passengers arriving into Ireland from Britain are being advised to carry out an antigen test every day for five days after arrival.

Dr Holohan said that early evidence is pointing to an increased transmissibility of the Omicron variant, though it is not clear whether this is because it is escaping the vaccine effect or is inherently more transmissible.

But he said that even if it is less severe, because it is more transmissible it can generate more cases "and paradoxically create a challenge in terms of the impact on public health and the health services".

Dr Holohan said that with 14 days to go until Christmas Eve, the measures taken now will help to reduce the risk posed to family gatherings.

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The Taoiseach said that offering the guidance in terms of advice rather than regulation is the "practical approach" taken by the Government.

"It's an extra protection for themselves and their families and their loved ones," Micheál Martin said.

"There is evidence of community transmission in the UK, mainly due to the fact that they have probably one of the best genome-sequencing programmes in Europe but, also, they’ve said that there’s community transmission."

The advice from the European health committee is to focus on testing, he said.

"Before you depart [from the UK to Ireland] take your test; when you arrive, now we’re saying as an extra precaution to protect yourself and others, take an antigen test on a daily basis."

Earlier, Minister for Finance Paschal Donohoe said the measure is guidance rather than a regulation.

Speaking on RTÉ's Today with Claire Byrne, he said the Government will not seek to enforce the measures, but would instead "trust our citizens to do the best thing by their health".

The overwhelming majority of people do implement public health guidance, Mr Donohoe added.

There have now been six cases of the recently discovered variant identified in Ireland. Dr Holohan that a number of other probable cases are under investigation.

The latest travel advice is aimed at encouraging people to take a cautious approach to international travel in light of the transmission of the new variant.

The Government is urging people to take account of their overall health, their vaccine status, and the spread of the variant in other countries before they decide to travel.

In a statement, the Government said anyone eligible for a booster vaccine should avail of it where possible, if contemplating international travel soon.

The current requirement for all overseas passengers to have a pre-departure Covid test will continue to apply.

Mr Donohoe has also said it is not inevitable that there will be a wave of Omicron Covid-19 infections in Ireland in the coming months.

Continuing with the efforts of the booster vaccine campaign and public health measures "gives us the prospect of minimising the challenges we may face at the end of the year and early next year", he said.

The Government is going to do all that it can "from a vaccination and support point of view", he said, while continuing to ask citizens to get their vaccines when they are offered.

The minister added that efforts will continue to scale up booster vaccines and provide more locations and IT resources to avoid recent difficulties at vaccination centres.

Meanwhile, there were 4,115 new coronavirus cases reported by the Department of Health today.

Additional reporting Mícheál Lehane