A record 11,182 new cases of Covid-19 have been reported by the Department of Health.
It is the highest number of cases reported on any one day since the pandemic began, overtaking the previous high of 8,248 reported on 8 January last.
The Department of Health has said it estimates that 83% of cases are due to the Omicron variant of the virus.
There are 393 patients with Covid-19 in hospitals, an increase of three since yesterday.
Of these patients, 89 are being treated in intensive care units - a decline of nine from yesterday and the lowest number since 9 November.
In Northern Ireland, a record number of cases has also been reported with the Department of Health confirming 3,286 new infections.
On vaccines, two million booster or third doses have now been administered, according to the chair of the High-Level Task Force on Covid-19 Vaccination.
In a tweet tonight, Professor Brian MacCraith also said that 400,000 doses were given out this week.
He paid tribute to all those involved in the vaccination programme.
Earlier, he told RTÉ's News at One that "the original target we set for Christmas was 1.5 million".
At the end of a remarkable week:— Brian MacCraith (@muirtheimhne) December 24, 2021
💉 >400k doses administered
💉 ~2m boosters/3rd doses now given
Gratitude is due to so many:
Vaccinator teams in VCs
GPs & Practice Nurses
& many more! 🙏 pic.twitter.com/e0PtBtC2O6
On 10 January, all other adults aged 16 to 29 will be able to avail of a booster vaccine, as well as children aged 5 to 11.
Those children with underlying health conditions will be offered the jab a week earlier.
Health Service Executive Vaccination Lead Damien McCallion said that Ireland's PCR testing system has come "under pressure in the past 48 hours" but will continue to operate throughout the Christmas period.
People seeking a test would be able to avail of one on Christmas Day and St Stephen's Day, he said, "albeit there will be a slightly reduced service".
Mr McCallion added: "I know it's difficult for people waiting for results but the advice remains the same, if you have symptoms you should isolate."
He said even if there appeared to be no PCR slots available on the website, people should keep monitoring it as "there will be slots available over the day as we look at the attendance rates and referral rates from GPs".
"We are now up at a record number of laboratory tests at over 235,000 in the past seven days."
Mr McCallion said people can use the "list your contacts" portal to help speed up the test and trace process for close contacts.
HSE updates guidelines on masks for healthcare workers
Healthcare workers are now required to wear FFP2 respirator masks when caring for patients in all healthcare settings, the HSE has said.
Respirator masks will also be offered to patients in multi-bed or open areas who are able to wear them.
The HSE also said that surgical masks should be worn by all healthcare workers for all interactions with colleagues in the healthcare setting where patient care is not delivered or maintained.
The Deputy Chief Medical Officer has warned that the incidence of Covid-19 is increasing across all age groups.
In a post on Twitter, Dr Ronan Glynn also said that if people "have even mild symptoms of a cold or flu then isolate and stay away from others."
Incidence of #COVID19 is now increasing across all age groups. Here are 5 things you can do to keep yourself & your loved ones as safe as possible— Dr Ronan Glynn (@ronan_glynn) December 24, 2021
1⃣If you have even mild symptoms of a cold or 'flu then isolate & stay away from others#ForUsAll
Everyone should restrict their movements if they live with someone who has a positive antigen or PCR test.
People who have arrived from overseas should do daily antigen tests for five days, he said.
If they test positive or develop any symptoms they should isolate and book a PCR test, Dr Glynn added.
He also urged people not to meet older or vulnerable people if they have already met with a lot of people this week.
"This is a difficult message at this time but is important if we are to keep each other safe," he said.