Five further cases of the Omicron variant have been detected in Ireland, bringing the total number here to six, as the Department of Health has reported 4,022 new coronavirus cases.

The number of people with the virus in hospital is at 530, a decrease of 13 since yesterday. Of these, there are 115 patients in intensive care, down three.

In a statement, the Chief Medical Officer has said that following the confirmation of the Omicron cases, a number of other probable cases are under investigation.

Dr Tony Holohan said: "Although this is a new variant, our early understanding gives us confidence that a booster dose of Covid-19 vaccine will offer good protection against Omicron and Delta infection.

"Our current wave of disease continues to be driven by the Delta variant of Covid-19. We know that the public health measures we are so familiar with will break the chains of transmission of Delta, and we are confident they will work on Omicron."

Dr Holohan urged people to continue following public health guidelines.

Meanwhile, passengers arriving from Britain are being advised by the Government to undertake daily antigen tests for five consecutive days, beginning on the day of arrival.

The advice was issued after the Government received an updated public health assessment of the Omicron variant.

It also urged people to take account of their overall health, their vaccine status, and the spread of Omicron in other countries before they decide to travel.

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

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

The Taoiseach earlier stated that he cannot say for certain that further restrictions will not be needed before Christmas.

Micheál Martin said the Government would have to follow what is happening with the new variant across the UK and Europe.

He said the coalition would always listen to public health advice and then make decisions.

"It's challenging but the early signs are that we are looking at a more infectious variant that may not, but the jury is well out on this, be as damaging from a disease perspective," he said.

Mr Martin said that once again the key metric would be admissions to hospitals and ICUs.

In relation to international travel, the Taoiseach said Ireland would align with the EU on travel policy.

He pointed out that the World Health Organization and the European Centre for Disease Prevention and Control are not advocating travel restrictions despite the challenges posed by the virus.

He said travel restrictions were not "the direction of travel" right now and the Covid test requirement introduced in Ireland last Sunday had already reduced the volume of international travel.

Health Service Executive CEO Paul Reid has said that public health measures, including wearing a mask, social distancing and ventilation, will continue for a "sustained and long period of time".

He told the HSE briefing: "We don't see people not needing to wear a mask or not needing to keep social distancing for some time to come."

Covid circulating in Ireland before first official case

A new study has confirmed the circulation of Covid-19 among Ireland's population before the first official case was announced in the country on 29 February 2020.

It follows a study of blood donations between February and September 2020.

The first antibody positive donor samples were confirmed on 17 February 2020 - two weeks before the first official case.

Significantly higher antibody levels for Covid-19 were found in Dublin compared to the rest of the country. The study is published in the Journal of Clinical Virology.

Meanwhile, the overall number of Covid-19 outbreaks reduced by 12 last week, according to new data from the Health Protection Surveillance Centre.

There were 139 outbreaks reported to last Saturday, down on the previous week.

There were 30 outbreaks reported in schools, 26 in residential institutions, ten in hospitals and ten in nursing homes.

As routine contact tracing ended in primary schools at the end of September, the outbreak figure for schools should be considered with this in mind.

An outbreak is two or more linked cases.

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Northern Ireland has today reported 1,819 new coronavirus infections and a further four deaths.

The Health Service Executive is expected to set out its plans following the recommendation yesterday by the National Immunisation Advisory Committee that children aged five to 11 years be offered a Covid-19 vaccination.

Some of the stocks of vaccine are expected to arrive next week when the first doses could be administered.

NIAC has said the HSE should consider setting up separate child-friendly Covid-19 vaccination clinics, which it said could help minimise distress and reduce the likelihood of vaccination error by having adult and paediatric doses at the same venue.

People aged 50 to 59 are now eligible for a booster vaccine.

Two drop-in clinics in Dublin reached full capacity after queues formed from early this morning.

Separately, the Department of Health has said that EU Digital Covid Certificates for booster vaccines are not currently being issued in Ireland.

French President Emmanuel Macron has said that Digital Covid Certs will not be valid without the booster vaccine included after 15 January 2022.

Additional reporting Mícheál Lehane, Fergal Bowers