The omicron variant, which has double the number of mutations compared to the delta variant, is highly contagious and has led to cases being found worldwide.
The UK confirmed the presence of omicron, which was first detected in South Africa, on Nov 27.
The doubling rate of omicron in some regions is now down to less than two days, and weekly hospitalisations are up by 10 per cent nationally, the Prime Minister said in a press conference on Wednesday 15 December.
Prof Chris Whitty, England’s Chief Medical Officer, said: "It looks as if delta which has been with us for a while is still flat, and the growth is omicron.
"So what we’ve got is two epidemics, on top of one another, an existing delta epidemic, roughly flat, and a very rapidly growing omicron epidemic on top of it."
However, the Prime Minister praised the public’s response to the Government’s booster drive.
Over 48 per cent of adults in the UK have been boosted, he confirmed, with a record number of 904,598 booster jabs administered on Saturday Dec 18 alone.
"Please get boosted now," he urged.
Below, we have answered the key questions about the variant, the vaccines, and what the future may hold:
What are the symptoms of the omicron variant?
Experts have warned that omicron is triggering a “rather different” set of symptoms compared to previous variants. The main symptoms of the omicron variant are being reported as:
- Other body aches (including lower back pain)
- Sore or "scratchy" throat
- Runny nose
An analysis of roughly 78,000 omicron cases in South Africa, published on Tuesday Dec 14, found that the variant is resulting in milder disease compared to previous waves, with 29 per cent fewer hospitalisations than the Wuhan strain and 23 per cent fewer compared to delta.
Sir John Bell, Regius Chair of Medicine at the University of Oxford and a UK Government advisor on Covid-19, added that the emerging data suggests omicron is "behaving rather differently" to previous variants, when speaking on BBC Radio 4’s Today programme.
How long before omicron symptoms appear?
The time it takes for a person infected with omicron to develop symptoms after exposure may be shorter than previous variants, current evidence would suggest.
This means that the "incubation period" – when you have the virus, and it is working its way through your system – could be as little as three days before symptoms appear.
How is this different to previous variants?
Emerging evidence indicates that omicron spreads more easily, which is resulting in a faster and higher peak than previous variants, even if immunity from severe disease continues.
Hospitals in South Africa are continuing to report "far milder" symptoms from omicron compared to previous variants. Dr Richard Friedland, the chief executive officer of Netcare, the largest private health care provider in South Africa, told The Telegraph that early trends during the country’s fourth wave indicated a "far less severe form" of Covid.
During the first three waves, 100 per cent of the 55,000 Covid-19 patients hospitalised in Netcare facilities needed oxygen. So far, during the new wave, only 10 per cent of 337 hospitalised patients need oxygen.
It was stressed, however, that these were only preliminary results and that the situation could change.
During a press briefing at Downing Street on Wednesday Dec 15, Prof Whitty said there should be "really serious caution" over reports that a reduction in hospitalisations was being seen in cases of omicron in South Africa.
He said: "The first caution on this is simply a numerical one – if the rate of hospitalisation were to halve but you’re doubling every two days, in two days you’re back to where you were before you actually had the hospitalisation.
"If the peak of this is twice as great, then halving of the size of the hospitalisation rate, you still end up in the same place. And this peak is going very fast."
He added: "The second point I wanted to make, which I’m not sure it’s fully been absorbed by everybody, is that the amount of immunity in South Africa for this wave – because of a prior Delta wave and vaccination – is far higher than it was for their last wave. And therefore the fact that there is a lower hospitalisation rate is unsurprising."
This sentiment was echoed by Dr Maria Van Kerkhove, technical lead of the World Health Organization’s coronavirus response, during a press conference on Dec 8, as she cautioned that reports of mild disease are anecdotal and it is "too early" to draw firm conclusions.
In an address on Dec 12, Boris Johnson warned of a "tidal wave" of omicron and said: "Do not make the mistake of thinking omicron can’t hurt you, can’t make you and your loved ones seriously ill."
What happens if I have omicron?
All contacts of new variant cases were originally told to self-isolate, but on Dec 8 it was announced that daily testing would be introduced instead for those who come into contact with infected people. All Covid contacts now have to take daily lateral flow tests, not just those who come into contact with omicron.
The UK Health Security Agency is continuing to carry out targeted testing at locations where confirmed omicron cases were likely to have been infectious.
What is the risk of reinfection with omicron?
A large-scale South African preliminary study, published on the Medrxiv website, surveyed nearly three million people infected with Covid. It found that the risk of reinfection from the omicron variant is three times higher than for the delta and beta strains of the virus.
The authors concluded: "Evidence suggests that the omicron variant is associated with substantial ability to evade immunity from prior infection."
Why is it called omicron?
Officials at the World Health Organisation skipped two letters of the Greek alphabet when naming the latest Covid variant in order to avoid "stigmatising" China, and perhaps its premier Xi Jinping.
A WHO source confirmed the letters Nu and Xi had been deliberately avoided. Nu had been skipped to avoid confusion with the word "new" and Xi had been ducked to "avoid stigmatising the region", they said.
Since May, new variants of Sars-COV-2 have been given sequential names from the Greek alphabet under a naming convention devised by an expert committee at the WHO. The system was chosen to prevent variants becoming known by the names of the places where they were first detected, which can be stigmatising and discriminatory.
Do vaccines protect against the variant?
Mr Johnson said on Dec 12 that two doses of a Covid vaccine are "simply not enough to give the level of protection we all need" from the "tidal wave of omicron coming".
"But the good news is that our scientists are confident that with a third dose – a booster dose – we can all bring our level of protection back up," he said.
On Dec 15, Prof Whitty reiterated the Prime Minister’s words, stating that the protection provided by the vaccines was going to be "eroded" because the current vaccines are "less well matched" to the omicron variant.
He added that the point of boosters was to replicate the previous level of protection.
This has been echoed by Professor Salim Abdool Karim, former chairman of South Africa’s ministerial advisory committee on Covid-19, who told the Telegraph it would take "weeks and weeks" to see if Pfizer and Johnson & Johnson vaccines will defend against the new B.1.1.529 variant.
Stéphane Bancel, chief executive of the vaccine maker Moderna, has himself predicted that there will be a "material drop" in the effectiveness of vaccines against the omicron variant, due to the high number of mutations in the spike protein, which the virus uses to latch on to human cells – but this is being disputed.
Do booster jabs protect against the variant?
Data from a government-funded Covboost trial, published in The Lancet, has found that booster jabs produce long-lasting T-cells that are likely to work against all current and future coronavirus variants, including omicron.
The scientist behind the Pfizer-BioNTech vaccination, Dr Ugur Sahin, has also said that he remains optimistic that the jab will provide protection against severe disease caused by omicron. He told the Wall Street Journal: "Our message is: Don’t freak out, the plan remains the same: Speed up the administration of a third booster shot."
Pfizer itself has said in a statement that three doses of the Pfizer/BioNTech Covid vaccine are effective against the omicron variant, adding that boosted individuals had the same level of protection as people received with two doses against the original form of the coronavirus.
Lab studies using blood samples of triple and double-jabbed individuals were infected with omicron and analysis revealed antibodies effectively neutralise the variant of concern
On Dec 12, Mr Johnson announced the launch of the Omicron Emergency Boost, "a national mission unlike anything we have done before in the vaccination programme".
He confirmed that all adults should get the third dose by the new year, bringing the previous target of boosting all adults by the end of January forward by an entire month, with the wait between the second and third doses being halved from six months to three.
And as of Monday Dec 20, 12- to 15 year-olds could book in for a second jab.
Prof Whitty has said it is not yet clear how regularly we will need to have booster jabs in the future.
Raising the boosters bar
But German research suggests that the latest variant can evade antibodies that are produced by booster jabs to a significant extent.
Sandra Ciesek, the director of the Institute of Medical Virology at University Hospital Frankfurt, stated on Dec 7 that early laboratory results showed boosters may not be a panacea against omicron.
Blood taken from subjects who had received three jabs performed better against omicron than those which had not been boosted, but was nevertheless much reduced compared to delta.
"BioNtech three months after booster only 25 per cent neutralising versus 95 per cent with delta," she wrote in a tweet. "Up to 37 times the reduction in delta vs. omicron."
What has WHO said about the omicron variant?
The World Health Organization has said that omicron has been detected worldwide, stating that the highly mutated variant could have a "major impact" on the trajectory of the pandemic.
Dr Tedros, head of WHO, told a recent press briefing: "Certain features of omicron including its global spread and large number of mutations suggest it could have a major impact on the course of the pandemic. Exactly what that impact will be is still difficult to know, but we are now starting to see a consistent picture rapid increase in transmission."
He urged governments to urgently take action to curb Covid transmission in the face of omicron and the still dominant delta strain.
"Even though we still need answers to some crucial questions, we are not defenceless against omicron or delta," he said. "The steps countries take today and in the coming days and weeks will determine how Omicron unfolds. If countries wait until their hospitals start to fill up, it’s too late. Don’t wait. Act now.
"We’re running out of ways to say this but we will keep saying it. All of us. Every government and every individual must use all the tools we have right now."
Tracking Omicron variant
Dr Tedos also warned that travel bans are unlikely to be effective to halt omicron’s spread now the new variant has been widely identified.
It comes as Maria Van Kerkhove, WHO’s technical lead of the Covid response, suggested that the emergence of an omicron-type variant was "entirely predictable" – particularly in light of vast imbalances in the global vaccine rollout.
She said reducing transmission and increasing vaccinations is key to ending the pandemic.
Dr van Kerkhove told a briefing: "This is one of the scenarios that is completely predictable. The virus has been evolving since the beginning. We cannot only focus on vaccination coverage.
"You hear us say it a lot: it is not in vaccines only. We need a comprehensive response to tackle this problem. And global problems need global solutions," she added. "We can only fight this virus in some countries, while others are fighting with their hands tied behind their back."
This article is kept updated with the latest advice.