Scientists have urged people not to panic over the news, as at least 11 cases of the strain, first identified in South Africa, have now been found in the UK.
Millions more people were made eligible for an extra jab yesterday as The Joint Committee on Vaccination and Immunisation (JCVI) advised that all adults aged 18 to 39 should be offered a booster dose, in order of descending age groups, to increase their level of protection.
The wait for a third dose was slashed from six months to three, after early evidence pointed towards higher antibody levels offering greater protection against Omicron, as it was also announced that teenagers aged 12 - 15 will now be able to get a second injection.
England’s deputy chief medical officer Professor Jonathan Van-Tam told a Downing Street briefing that coronavirus variants were inevitable and Omicron was the “new kid on the block for now” but suggested the UK was in “uncharted territory” as to whether it would take hold.
He added: “I think it’s true to say that scientists around the world, not just in the UK, unfortunately agree that this one is of increased concern.”
“I do not want people to panic at this stage,” Professor Van-Tam said.
“If vaccine effectiveness is reduced, as seems pretty likely to some extent, the biggest effects are likely to be in preventing infections and, hopefully, there will be smaller effects on preventing severe disease.”
Health Secretary Sajid Javid also acknowledged the new variant being “on the offensive”, but said that expanding the vaccine programme will “protect more people more quickly, and make us better protected as a nation”.
From today, masks will be compulsory in shops and on public transport again in England, and there will be tighter restrictions for people coming into the country.
All arrivals will now need to take a PCR test - rather than a cheaper lateral flow - on or before their second day, and will need to isolate until they get a negative result.
In addition, anybody who is a close contact of a suspected Omicron case - regardless of their vaccination status - will also need to self-isolate if contacted by NHS Test and Trace.
Prime Minister Boris Johnson described the new rules as “proportionate and responsible” and said they will “buy us time in the face of this new variant.”
“Not only will today’s steps help us slow down the variant’s spread,” he said.
“But they will help us protect each other and the gains we have all worked so hard for.”