CASES of Omicron are likely to be five times higher than those 246 confirmed, an expert has said.
Professor Paul Hunter said the super mutant Covid strain would “probably be dominant” in around a month, overtaking Delta.
The professor in medicine at the University of East Anglia said there were probably more than 1,000 cases in the UK at the moment.
And there was current concern that Omicron “is spreading rather more quickly than the Delta variant”.
The UK Health and Security Agency (UKHSA) said a further 86 cases of Omicron had been confirmed in the UK on Sunday, 68 in England and 18 in Scotland, bringing the total to 246.
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 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.
“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, and 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 against the dangerous strain.
But vaccines 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”.
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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