But so much remains unknown about the new variant. Here’s what we’ve learnt so far.
What is Omicron?
Omicron is a Covid “variant of concern” which was first flagged by South African specialists and then named by the World Health Organisation (WHO).
It’s not yet known how deadly this particular strain is compared to previous ones such as Alpha and Delta.
By Friday, 42 cases of Omicron had been found in the UK.
People who test positive for Omicron have displayed the following symptoms:
Mild muscle aches
Unlike with the Delta strain, patients have not yet reported a loss of small or taste. There has not been a reported drop in oxygen levels among infected individuals either.
Last Sunday, the WHO said: “There is currently no information to suggest that symptoms associated with Omicron are different from those from other variants.”
How dangerous is it?
The symptoms reported so far have ranged from mild to severe disease, according to the WHO, making it hard to define how dangerous Omicron really is.
Dr Maria von Kerkhove from WHO believes Omicron may be more transmissible than previous variants, based on the rising number of cases in South Africa where this new strain was first detected.
However, she said there was still a question mark over whether it was more transmissible than the world’s current dominant strain, Delta.
Impact on vaccines
Scientists are yet to find out just how effective any of the vaccines are against this new strain, as they were all developed against the Delta variant.
While specialists behind the Oxford-AstraZeneca and the Pfizer-BioNTech jabs suggest the vaccines will still be able to keep severe disease away, Moderna’s CEO Stephane Bancel disagreed.
He pointed out that most of the mutations in the Omicron variant occurred on the spike protein, which is used by the Covid vaccines to boost the immune system.
He told the Financial Times this meant there would be “material drop” in the effectiveness of the jab.
He said: “There is no world, I think, where [the vaccines’ effectiveness] is the same level we had with Delta.”
However, the UK has already announced that all adults aged 18 and over will be able to get their third jab soon.
Although the exact effectiveness of the current vaccines against Omicron remains unknown, some experts claim the shots should still prevent hospitalisation and death – even if it does not stop infection.
Britain has now ordered an extra 114 million Covid boosters so that other booster jab campaigns can be unrolled at short notice if another “variant of concern” makes its way to the UK.
What does WHO say?
The WHO says the health risk from Omicron is “very high”.
It has made it clear that more data is needed before it can confirm the transmissibility of the variant, the severity of the disease and just how it responds to the vaccines.
The WHO has also blamed richer nations for not distributing vaccines around the world for the emergence of the new variant.
The organisation said scientists should know more about the variant “within days, not weeks”.
New Covid rules
Downing Street called a press conference on the day that WHO identified the variant and announced “temporary and precautionary” rules were being brought in to get ahead of this new strain.
International travel rules have changed too, with more southern African countries added to the red list. People arriving into the UK need to take a PCR test on the second day of their return.
The rules will be reviewed after three weeks, shortly before Christmas. Health secretary Sajid Javid has emphasised that if Omicron is no more deadly than Delta, the restrictions will be lifted.
Prime minister Boris Johnson has encouraged the public to continue socialising and to carry on with their Christmas plans.