During a press briefing at Downing Street on Dec 15, Sir Chris 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, Sir Chris 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.