Northern Ireland's Chief Medical Officer says he is more concerned now than at any stage of the pandemic.
The rate of growth of the Omicron variant, Dr Michael McBride says, is "extremely concerning" as its wave is headed towards Northern Ireland.
And while the message is for the public to "double down" on existing measures, those in place at present may not be enough, he warned.
Speaking to the media on Tuesday afternoon, Dr McBride said: "It is increasing very, very rapidly and is extremely infectious. It is therefore important that we all double down on the existing measures that we have in place.
"However, I think it is fair to say that those existing measures may not be sufficient and as the First and Deputy First Minister have said, they are absolutely committed to ensuring our health service isn't overwhelmed.
"What we will be doing is keeping the situation under very close review, looking at what's happening in neighbouring jurisdictions and providing the best advice that we can to the Executive to control this wave of Omicron which is coming towards us."
Dr Michael McBride added: "The new variant of Covid-19, Omicron, is highly infectious and is spreading very fast. Soon it will become dominant in Northern Ireland. We are likely to see a very significant increase in cases of Omicron in the run up to Christmas, that's not unexpected and I think we will see that reflected in reports over the coming days.
"There's cause for very significant concern at this time. We still don't have some key elements of information but I have to say, I am more concerned at this stage than I have been at any stage in the pandemic. Until we know that information, I would ask the public to exercise caution and follow all of the advice.
"We need to get as many people boosted, as we possibly can before we see the peak of the Omicron wave."
Prof. Ian Young told the Covid media briefing "unfortunately Omicron presents a new threat" as they know that it is significantly more transmissible.
"It is probably around two and a half times more transmissible than the Delta form of the virus," Professor Young said.
"We know that previous immunity, whether from natural infection with Delta, or from vaccination, gives somewhat less protection against Omicron.
"If we look at that is happening elsewhere in the UK and internationally, we see that once Omicron becomes established, it spreads remarkably quickly. The doubling time for cases is around two days in both England and Scotland. It is inevitable that we are going to see the same thing in Northern Ireland.
"As a result of that, we'll see increasing case numbers of the Omicron virus and they're likely to increase very rapidly. It's probably going to become the dominant form of the virus before the end of this year, possibly earlier than that.
"There are some significant levels of uncertainty which remain. The most importance of those is the severity of infection and the extent which it leads to hospital admission and serious disease.
"This is a very concerning situation and one that we are worried about and need to keep an extremely close eye on.
"The situation is moving really rapidly and people are likely to be surprised by the speed at which Omicron cases will increase.
"If those cases don't lead to much in terms of hospital admissions, then the case for restrictions becomes much less. If it appears that for example, Omicron has similar severity to Delta in terms of risks of hospital admission, then the consequences of a very large wave of cases occurring rapidly should be apparent to everybody in terms of the likely hospital pressures."
The number of confirmed cases of the Omicron variant of COVID-19 has reached 151 in Northern Ireland.
This is a significant increase in numbers due to "rising community spread" says the Public Health Agency, as well as a change in definition across the UK from today which has meant that cases that were previously recorded as ‘highly probable’ are now automatically recorded as 'confirmed'.
Dr Brid Farrell, Deputy Director of Public Health at the PHA, said: “The identification of more cases of this variant in Northern Ireland is not unexpected, but it does act as a timely reminder that each of us needs to do what we can to slow its further spread and help protect ourselves and those around us.
“The confirmation and identification of this variant demonstrates that PHA surveillance systems and the Contact Tracing Service are working. It re-enforces the need for continued vigilance and adherence to public health guidance. It is essential that people continue to work within the regulations and advice, and get fully vaccinated.
“We know that the vaccine booster can significantly increase protection against Omicron, and local health services are undertaking a huge upscaling of the booster programme to support this. If you are eligible to receive the booster, please get it. If you haven’t yet had your first or second jab, please don’t delay in getting them as advised."
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