Speaking on the Christmas lockdown issue, Raab told BBC: "We can't make hard fast guarantees."

The booster rollout makes tougher restrictions "much less likely" though - but "it depends on the severity of Omicron", Raab adds.

Meanwhile, the Irish Department of Health on Sunday reported 5,124 new confirmed COVID-19 cases, saying that about 52 percent of them were due to the Omicron variant.

"It has taken less than two weeks for Omicron to become the dominant strain of COVID-19 in Ireland, revealing just how transmissible this virus is," said Tony Holohan, chief medical officer with the department, in a statement.

He urged all the people eligible for a booster vaccine to get it as early as possible, saying that "it is extremely important we do everything we can to flatten the curve of this wave now to prevent unnecessary deaths, risk to the vulnerable and to protect our health service."

Starting from Sunday, people aged 40 to 49 in Ireland are eligible for a booster vaccine. Local media reported that long queues were seen in many vaccination centers across the country.

The Irish government originally planned to inoculate the people in this age group with the booster vaccine starting from Dec. 27, but has decided to vaccinate as many people as possible before the coming Christmas and New Year holidays, according to the Irish health department.

The Irish government on Sunday also announced in a statement that Eamon Ryan, minister for environment, climate and communications and minister for transport, and also the leader of the Green Party, has tested positive for COVID-19 and "is self-isolating at home."

Ryan "attended Cabinet remotely on Friday, so members of the Cabinet are not close contacts," said the statement.