Confirmed cases of Omicron, the new more infectious Covid-19 variant, are so far concentrated in three counties, it emerged yesterday.

The six genetically analysed cases include four in Co Meath, one in Longford and one in Dublin.

It comes amid fears the real scale of the spread of the variant across the country is much higher.

The National Virus Reference Laboratory is set to increase the number of coronavirus samples that need to undergo genetic analysis to confirm whether they are the new variant, from 1,500 to 2,000 a week.

The World Health Organisation (WHO) has called on countries to step up surveillance to track the spread of behaviour of the Omicron variant.

The HSE saw another big turnout of people in their 50s and 60s at walk-in booster ­vaccination centres.

More walk-in booster slots were added to the Citywest centre in Dublin, but the Waterford IT Arena had to declare full capacity yesterday evening and turn away some walk-ins with a queueing time of around two-and-a-half hours.

More walk-in vaccination clinics will open across the country today with more than 1.1 million people now with a top-up dose.

HSE chief Paul Reid confirmed yesterday the opening times for walk-in booster ­clinics would be extended.

The plan is to have everyone in their 60s or 50s boosted, or with an appointment for a booster jab, by the end of this month.

However, Christmas socialising remains a concern with so much still unknown about the Omicron variant which, even if it causes less serious disease, could lead to another rise in hospitalisations.

There were 4,115 new cases of coronavirus reported yesterday with 511 Covid patients in hospital, a drop of 19. The number in intensive care stood at 110, a reduction of five in a day.

Taoiseach Micheál Martin, who is 61, joined the queue at Cork City Hall yesterday where he got his booster shot.

“We can overcome this wave as well – but we have to behave sensibly, assess it as we get more information and deal with the challenges. I am concerned but I am also hopeful,” he said. “Twelve months on, I have received a booster vaccine that illustrates the capacity of science and our system to respond to the demands of this pandemic.”

He hopes that 1.5 million people will have boosters or additional doses by Christmas. This would mean another 400,000 boosted in the next two weeks.

Antiviral medicines that aim to prevent hospitalisations in people with Covid were on their way, he added.

Mr Martin specifically urged people travelling from the UK to abide by advice to use antigen tests five days after coming here.

“It is because of Omicron but, let’s be honest, there is also a higher volume of traffic between the UK and Ireland.

“I am concerned about the Omicron variant because of the high volume that might emerge here post-Christmas or even in the next couple of weeks. Its doubling time seems to be shorter.”

He added that “a week is a long time in Covid-19”.

Referring to the possibility of more restrictions he said: “One can never rule out anything in relation to Covid-19 because there are so many twists and turns. But what is important is that we adhere to the guidelines that are in place and the restrictions that have been brought into play.”

Chief medical officer Tony Holohan warned that with a two-week countdown to Christmas day, Ireland was in a “very uncertain and unstable position due to the high incidence of Covid-19”.

He said the current high level of cases was being driven by the highly transmissible Delta variant. “This is a matter of very significant concern as we wait for more evidence relating to the Omicron variant, and the impact it may have, to emerge,” Dr Holohan said.

“At the moment, based on the evidence available to us, we believe that the public health measures we are so familiar with will work to slow and stop the transmission of the Omicron variant, as well as the Delta variant.

“Early indications suggest that a booster dose of Covid-19 vaccine will offer good protection against infection from Delta and Omicron.”

He urged people who were eligible for a booster to avail of the jab. “Similarly, if you are yet to receive a primary dose of Covid-19 vaccine then please come forward as soon as possible.”

He said Christmas was a time for getting together with family and friends.

“You can take measures today and in the next few days that will ensure the safest possible interaction with your loved ones over Christmas.

“Risk assess the environments you plan to be in over the next two weeks – consider if they offer the opportunity to protect yourself with each layer of the public health advice.

The basics including avoiding crowds and reducing contacts. Wear a mask including in crowded outdoor environments. Keep a distance and if you feel unsafe in a situation leave. Open windows and avoid poorly ventilated indoor spaces and wash hands ­regularly.”

Meanwhile, the impact of Covid-19 on hospital waiting lists showed a worrying backlog with more than 897,000 now waiting to be treated or assessed by a consultant – an increase of 58,000 so far in 2021.