A fortnight ago, health officials in South Africa were preparing to report a concerning, unfamiliar variant of coronavirus to the World Health Organisation.
The UK swiftly slapped travel bans on South Africa and its neighbouring countries, but on Monday health secretary Sajid Javid confirmed the strain, now known as Omicron, has begun circulating within communities across England.
As national Omicron numbers increase, ITV News outlines what you need to know about the variant.
What is Omicron?
Omicron is a strain of coronavirus with more mutations than prior variants have had. Possibly 30 are in a key place - the spike protein that lets the virus attach to human cells.Scientists recognise a few mutations from earlier variants that were more contagious or a bit resistant to vaccination. But they’ve never seen this particular constellation of changes.
Most “are really unique to this virus,” said Dr. William Moss of the Johns Hopkins Bloomberg School of Public Health in the US.
“It’s that combination of potential increased transmissibility and ability - potential ability - to escape our immune system that has everyone worried.”
On Tuesday, Boris Johnson said the "early signs" show Omicron is more transmissible than the Delta variant. How widespread is it?
Although it was first reported by South Africa, the variant has now been detected in numerous countries across the world.
As of December 7, Omicron had been detected in 38 countries, as far apart as Japan, Australia, Nigeria and Brazil.
Scientists across the world are seeking to track Omicron's movements through genomic sequencing, i.e. using laboratory analysis to identify a virus's genetic make-up.
How many deaths and hospitalisations has Omicron caused?
As of December 3, world health authorities had yet to link any deaths to Omicron. However, not all Covid tests currently assess Covid-19 samples for Omicron.
South Africa, where Omicron has achieved near dominance, has reported hospitalisations linked to the variant. However, officials have added that most cases seem to have been relatively mild.Does the vaccine work against it?
Experts do not yet know how much Omicron might evade immunity from past Covid illness or vaccines.
On Tuesday, Boris Johnson's spokesman echoed statements from health officials, saying: “At this stage it is too early to tell, it remains the case that we don’t have that data.”However, Pfizer and BioNTech said that in the event of a variant which could escape the effects of the vaccines, the firm expects “to be able to develop and produce a tailor-made vaccine against that variant in approximately 100 days, subject to regulatory approval”.
BioNTech, the company behind the western world's most widely used Covid vaccine, said it expects more data on the new variant within two weeks to help determine whether its shot would have to be reworked.
What precautionary action has the UK already taken in relation to the variant?
Face-coverings have become mandatory in shops and on public transport in England. Passengers travelling to the UK must take a pre-departure Covid-19 test and get a negative result before arriving in the country, the government has announced.
In addition, contacts of people who have tested positive for the Omicron variant must self-isolate for 10 days, regardless of their vaccination status, and booster vaccines are being rolled out to more people.
Additionally, South Africa, Botswana, Eswatini, Zimbabwe, Namibia, Lesotho, Angola, Mozambique, Malawi, Nigeria and Zambia have all been put on the travel red list.
Anyone who arrives into the UK from one of these countries must quarantine in a government-approved hotel for 10 days at a cost of £2,285 for one adult.