CASES of Omicron are likely to be five times higher than those 336 confirmed, an expert has said.
Professor Paul Hunter said there was current concern that Omicron “is spreading rather more quickly than the Delta variant”.
It is therefore "probable" the super mutant Covid strain would be dominant in around a month.
According to the latest data, there are now 261 confirmed cases in England, 71 in Scotland and four in Wales, bringing the total number of confirmed cases across the UK to 336.
Due to a time lag between exposure and test results, it may be that there are several hundred more infected who are not aware.
Cases may also be underreported because Omicron is only detected in tests that are genetically sequenced.
Just a fraction - 25 per cent - of all positive tests are screened for identification of variant.
UKHSA has already warned the mutant variant is “transmitting rapidly and successfully" after first being identified here a week ago.
Prof Hunter, professor in medicine at the University of East Anglia, said there were probably more than 1,000 cases in the UK at the moment.
He told BBC Breakfast: “How it’s likely to spread in the UK still uncertain, but I think the early signs are that it will probably spread quite quickly and probably start outcompeting Delta and become the dominant variant probably within the next weeks or a month or so at least.
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“The big remaining question is actually how harmful it is if you do get Covid with this Omicron variant, and that’s the question that we’re struggling to answer at the moment.”
Prof Hunter said it was not clear how evidence from South Africa would translate to the UK as we have a highly vaccinated population.
🔵 Read our Omicron variant live blog for the latest news
South Africa first alerted the world to Omicron on November 23 and has begun experiencing a sudden four wave.
The earliest detection of Omicron was on November 8 in the Gauteng province, which includes the cities of Pretoria and Johannesburg
Within less than a month, it has become the nation’s dominant strain in circulation, accounting for 73 per cent of cases genetically sequenced.
It’s given scientists the indication that Omicron is able to outcompete Delta, possibly due to transmission advantages.
Experts have also discovered that people who have previously been infected with Covid may catch Omicron, a signal that vaccine protection will also be weaker.
It would potentially see hospitalisation rates go up - and put the NHS in a "very difficult position", the president of the Royal College of Emergency Medicine has warned.
Dr Katherine Henderson said that hospitals were already struggling to cope as Christmas approached and that a sudden increase in admissions could push services over the edge.
She said: "It is pretty spectacularly bad now, it will get worse - and if the new variant becomes a thing in terms of numbers and translates into hospital admissions we are going to be in a very, very difficult position.
"We still want patients to come but we do have to help people to understand that really at the moment the service is so stretched that an extra push could be very very difficult."
PLAN TO FIGHT OMICRON
Jabs are still the best protection against Covid, and are at the centre of the Government’s plan to fight Omicron.
Ministers have also signed off tough travel restrictions against a number of African countries, the latest being Nigeria where three cases of Omicron have been found.
Prof Hunter said travel restrictions would have a minor impact, adding that “one of the problems with travel restrictions” is that it can trigger countries to lie about their case numbers.
He said: “So I think once the infection is spreading within a country, then border restrictions don’t really add anything.
“We’ve known that long before Covid. This has been knowledge that we’ve had for decades, if not centuries, to be honest.”
It comes after Professor Mark Woolhouse, a Government scientific adviser, said the Omicron variant is already “spreading pretty rapidly” and the new travel measures “may be a case of shutting the stable door after the horse has bolted”.
He said although the numbers of people with the Omicron variant are “still quite small” and likely remain in the hundreds, they are “growing quite fast”.
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However, he insisted that vaccinations will still be “very, very good” at protecting against the new variant.
But Boris Johnson has denied the allegation travel measures were too slow and said the UK was the first country to take “decisive measures”.
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