Over 20,000 cases were confirmed by health officials yesterday, but the Chief Medical Officer said the true figures are likely to be much higher.
He said the high incidence of the virus in the community and the resulting constraints on the testing system has led to shift in advice for testing and isolation.
Dr Holohan said that it is no longer safe for four households to meet up indoors, despite official government advice which allows for limited indoor gatherings.
“We’ve seen a significant surge in infection and that surge in infection has continued unabated,” he told RTÉ’s
Morning Ireland programme.
“We have in excess of 20,000 cases announced yesterday. We think because of the constraints in our testing capacity that if we didn’t have those constraints, we might have had as many as 30,000 cases picked up yesterday.
“Meeting up in large numbers of four households at this point in time, given the levels of infection that we have is simply not safe, and I think it’s important now for people to hear that message.”
Dr Holohan said he has been in communication with the Health Minister Stephen Donnelly in recent days and Mr Donnelly shares the view that indoor gatherings should be avoided.
Last evening the Department of Health said people aged from four to 39 should use antigen tests if they suspect they have Covid and only seek a PCR test from the HSE if they get a positive antigen result.
Dr Holohan said the change in advice came about because the country’s PCR testing system is under intense pressure and people in higher-risk categories need to be prioritised for testing.
“We prioritised those to be people who are most at risk in terms of any underlying illness or by reason of age for the severe effects of the disease and those people who are clinically unwell.
“We need to ensure that we protect our PCR capacity for that primary purpose,” he explained.
Earlier this year, Nphet was slow to recommend the use of antigen tests with Prof Philip Nolan even comparing the rapid tests to “snake oil”.
However, Dr Holohan described the new advice on antigen tests as a “planned change” and said the incidence of the virus in society now warrants their use.
“In situations where the incidence of the disease is likely to be high we would always recommend an antigen test – that’s why they have always been used in outbreak situations,” he added.
Dr Holohan said people should conduct antigen testing at home over a number of days and if they get a positive rapid test result, they should then come forward for a PCR test.
Health officials have confirmed that the new Omicron variant now accounts for 90pc of all cases and Dr Holohan said if someone has any flu like symptoms they should isolate immediately and if someone they live with has symptoms, they should begin restricting their movements.
He explained that the high transmissibility of the new strain means that if one person in a household gets the virus, then there is a high chance of the whole household becoming infected.
While some evidence suggests that the new variant is less harmful then previous strains, Dr Holohan said health officials are still concerned about the pressure which hospitals could come under if case number surge further.
He said while the numbers in ICU are “somewhat stable” there has been an increase in general Covid-19 hospitalisations in recent days.
The CMO confirmed that there is still a “substantial proportion” of Covid-19 patients in hospital who are not fully vaccinated, and he urged everyone who can get a vaccine or a booster to come forward for one as soon as possible.
“The boosters and the vaccines for people who have had them, give significant protection against severe disease if you do in fact pick up this infection.
“If we had these levels of infection without that protection in terms of vaccination, we would see many, many more people in hospital and many more people in ICU,” he added.
Meanwhile, in terms of the return of schools next week, Dr Holohan said the current advice is that they should reopen but the situation is being monitored.
He said data showed that case numbers were falling among school-aged children at the start of December, but steps can be taken if necessary.
“At the moment schools are set to reopen next week… we’ll keep that whole situation under review. We’ll stay in close contact with our colleagues in the Department of Education as we’ve done all the way through this,” he said.
His comments come as another leading Nphet member said the country is in the “largest wave of infection we have ever faced”, but the “vast majority of infections” are not progressing to severe disease thanks to vaccines.
Prof Nolan has warned, however, that the scale of infection requires everyone to be “very cautious” and “to continue to slow this down”.
In a message posted on Twitter, Prof Nolan said the seven-day average of over 11,000 cases per day is “rising rapidly”.
Yesterday, over 20,000 new infections were reported, but Prof Nolan said if testing could fully keep pace with rising infections, daily case counts would be around “40pc higher”.
“Hospital admissions and numbers in hospital are increasing, and the rate is concerning; numbers in ICU remain stable for now. It will be at least another week before we fully understand how this wave of infection will translate into severe outcomes in our population,” he wrote.
He described the current situation as a “time for the greatest possible caution” and said people should get a booster vaccination, stay safe, protect each other, and limit social contacts to a minimum to delay the spread of Omicron in the coming days and weeks.
“Self-isolate if symptomatic and get a test. Restrict movements and test as advised if a close contact. Do not run the risk of infecting those you love. If you have no symptoms or restrictions, prioritise, and limit your contacts, and reduce the risk of those contacts.”
He added that to reduce the level of risk, members of the public should: “Consider meeting outdoors, shorten time, avoid crowds and crowded spaces, ensure adequate ventilation, maintain physical distance, wear a mask, keep good hand hygiene. If you are meeting vulnerable people, all the above, and consider serial antigen testing.”