Covid-19 cases are surging among people aged 16 to 34, the Republic of Ireland's Chief Medical Officer Dr Tony Holohan has warned.
Speaking on Wednesday, he said Ireland will see a significant rise in cases as the Omicron variant continues to spread across the country.
He also indicated that if cases do surge, the testing system will come under strain.
Like previous waves, the virus is spreading first among young people, Dr Holohan said.
“It is most dramatically increasing in those age groups at this point in time,” he said. “That is consistent with what we’re seeing in other European countries.”
He stressed he is not “pointing the finger” at young people, but said it is a fact of the pandemic.
Since Monday, all restaurants, bars and cafes have had to shut their doors at 8pm.
Indoor events have a limited attendance to 50% of capacity or 1,000 people, whichever is lower.
Outdoor events are also limited to half capacity, to a maximum of 5,000 people.
The Chief Medical Officer urged anyone not vaccinated, or waiting to get a booster jab, to come forward.
“Don’t put off the opportunity to be vaccinated if it comes your way,” Dr Holohan said.
The Irish Government and health officials have said a booster jab should offer more protection against severe disease if someone is infected with Omicron.
On Tuesday, 5,279 cases of the virus were reported by the Department of Health.
Earlier, HSE chief Paul Reid said 108,000 vaccines were administered on Tuesday.
On Twitter, he said 1.77 million booster and third doses have now been provided in the Republic of Ireland.
Dr Holohan, who has been urging people to reduce their social contacts over Christmas, said health officials are still waiting for more data on the new variant to emerge.
“While we do hope the pattern of severity will be much less than Delta, there is not enough data seen yet in Europe to conclude that,” he told RTE radio.
He also warned that “paradoxically”, a less severe but more transmissible variant would still cause major pressure for the health system.
“Increased transmissibility alone represents substantial risks for us in terms of pressure on our health system,” Dr Holohan said.
The Chief Medical Officer also said he does not believe his recommendations calling for tighter restrictions were leaked last week by the National Public Health Emergency Team.
Asked about the impact leaks have on businesses and the public, he said: “Finding out in that way is no way for anyone to find out.”
