A booster dose sees the risk of symptomatic infection with the Omicron variant “significantly reduced”, according to health officials who have urged all those eligible to make sure they get their third jab.

It comes as the experts warned the new variant could become the dominant strain in the UK by mid-December, with a Cabinet minister saying everything is being kept “under review” in terms of measures to tackle the spread.

Analysis by the UK Health Security Agency (UKHSA) found that the AstraZeneca and Pfizer-BioNTech vaccines provided “much lower” levels of protection against symptomatic infection with Omicron compared to Delta.

But the preliminary data, which looked at 581 people with confirmed Omicron, suggested effectiveness seemed to “increase considerably” in the early period after a booster dose, giving around 70 to 75% protection against symptomatic infection.

The findings come as daily Covid-19 cases reached their highest level in almost a year and the UKHSA predicted that, if current trends continue, the UK will exceed one million infections by the end of the month.

Cabinet minister Michael Gove warned of a “deeply concerning situation” after holding a Cobra meeting on Friday afternoon to discuss the latest data and the co-ordinated response across the four nations.

The Government said, as of 9am on Friday, there had been a further 58,194 lab-confirmed Covid-19 cases in the UK.

The last time a higher daily figure was reported was on January 9, when 59,937 cases were recorded.

An additional 448 confirmed cases of the Omicron variant have been reported across the UK, bringing the total number to 1,265.

Dr Mary Ramsay, head of immunisation at the UKHSA, said while their early data should be treated with caution, it indicates that “a few months after the second jab, there is a greater risk of catching the Omicron variant compared to Delta strain”.

She added: “The data suggest this risk is significantly reduced following a booster vaccine, so I urge everyone to take up their booster when eligible.”

Covid-19 case rates in UK nations
(PA Graphics)

Speaking to broadcasters, Mr Gove said the Omicron variant is doubling every two to three days in England “and possibly even faster in Scotland”.

He added that 30% of reported cases in London are the new variant, and warned that evidence suggests Omicron is “more likely” than past Covid variants to “potentially” lead to hospital admissions among the fully vaccinated.

Scotland’s First Minister Nicola Sturgeon has warned of the possibility of a “tsunami of infections” from the new variant – and said she could not rule out more restrictions north of the border as a result.

But No 10 maintained that there were “no plans” to go further with measures in England, amid reports that proposals are being drawn up for a Plan C, featuring even tougher rules.

Mr Gove said the current approach being taken is “proportionate”, but acknowledged that “we absolutely do need to keep everything under review”.

He said: “Action is absolutely required and, as new data comes in, we will consider what action we do require to take in the face of that data.”

The Guardian reported that Health Secretary Sajid Javid had been given a presentation from the UKHSA earlier this week warning that even if Omicron leads to less serious disease than Delta, it still risks overwhelming the NHS with 5,000 people admitted to hospital a day.

It said the leaked advice said “stringent action” would be needed on or before December 18 if the variant’s doubling time stays at 2.5 days, although the newspaper added that what such restrictions might entail were not set out other than to say measures that would bring the R number – representing the average number of people each Covid-19 positive person goes on to infect – below 1.

Professor Neil Ferguson, from Imperial College London, whose data was instrumental to the UK going into lockdown in March 2020, told The Guardian that projections suggest Omicron could “very substantially overwhelm the NHS, getting up to peak levels of admissions of 10,000 people per day”.

He said such a figure could be reached “sometime in January” but added that it was based on assumptions around the variant’s ability to get around existing protection, and the premise that it is similar to Delta in terms of the severity of disease it causes – something that is not yet known.

He said: “Even the best-case scenarios involve several-fold more admissions per day than we’re getting at the moment – we are at about 700 right now.”

New guidance expected to come into force from Wednesday will see care home residents allowed only three visitors and one essential care worker, as part of new measures to protect the sector from the spread of the new variant.

People must wear face coverings in more settings such as cinemas and theatres (PA)
People must wear face coverings in more settings such as cinemas and theatres (PA)

The Department of Health and Social Care (DHSC) said the move was “in order to balance the current Covid-19 risk and the need to keep people safe in line with clinical advice”.

From Friday, in England the legal requirement to wear masks was extended to more indoor spaces including museums, galleries and community centres.

There will be a return to working from home guidance from Monday, and mandatory Covid passports for large venues from Wednesday.

The new regulations will be put to a debate and vote in the Commons next week – and with Labour’s support they are certain to be approved despite the prospect of a large Conservative revolt.

Asked about the expected Tory rebellion, Mr Gove said he is “confident”  people will examine the proposals “seriously, soberly and thoughtfully”, adding: “And I’m also confident people will conclude that, on balance, it is right to act.”