Five times more Covid-19 testing each day is needed in Ireland to try to control the spread of the virus, according to a virologist at UCD.

Assistant Professor of Virology Gerald Barry said he was concerned the Omicron variant could causes case numbers to shoot upwards and described the preliminary data from South Africa as "troubling".

He said caution is needed about the anecdotal suggestion that Omicron is causing a milder disease.

Dr Barry also said it is frustrating to see Ireland enter back into a cycle of increased restrictions, without dramatically increasing testing and tracing efforts.

He said that Covid-19 testing needs to be multiplied by a factor of five and there should be contact tracing in all situations, including in schools.

Speaking on RTÉ's Brendan O'Connor programme, Dr Barry said Ireland is under-testing the population and so there is no clear picture of where transmission is coming from, resulting in tougher restrictions.

He said Ireland is in a much better position in relation to Covid-19 this winter compared to last year, but more planning for what lies ahead is needed.

He said the Government needs to plan for any "what ifs" that could arise if a third dose of vaccine does not afford enough protection against Omicron.

The Department of Health has reported a further 5, 156 cases of Covid-19.

There has been a slight rise in the number of people in hospital with Covid-19.

As of 8am, there were 503 patients with the virus, up 16 on the same time yesterday.

There are 110 patients in ICUs with Covid-19, down four on yesterday.

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Separately, Irish passengers will not require a negative Covid-19 test before travelling to the UK, after new rules were announced by the British government yesterday evening.

From Tuesday, all inbound passengers to the UK, from outside the Common Travel Area, will be required to produce a negative antigen or PCR test result.

The British government said it was intended to be a temporary measure following new data showing an increase in the number of cases of the new Omicron variant linked to foreign travel.

People travelling from within the UK or from Ireland, the Channel Islands or the Isle of Man do not have to fill out a passenger locator form, take any Covid tests or quarantine on arrival in England.

But these exceptions only apply to those who have not been outside the Common Travel Area in the previous ten days.

Latest figures from the UK Health Security Agency (HSA) showed as of yesterday, a further 26 cases of the Omicron variant had been reported across the UK - taking the total so far to 160.

In a further move the British government said that Nigeria was being added to the travel red list after 21 cases of the Omicron variant in England were linked to travel from the west African nation.

From 4am on Monday only British and Irish nationals and residents travelling from Nigeria will be allowed into the country and must isolate in a government-managed quarantine hotel

Separate measures have come into force in Ireland for all arriving passengers.

Anyone arriving into ports and airports from today will be required to present a negative PCR or professionally administered antigen test result.

In Northern Ireland, the Department of Health has reported a further 1,422 Covid-19 cases and seven deaths.