All people aged 18 and over are to be offered a Covid-19 booster vaccine.

It forms part of efforts to tackle the spread of the new Omicron variant, of which eleven cases have now been confirmed across the UK.

Millions more people in the UK will become eligible for a third booster dose after early evidence suggested that higher antibody levels may protect better against the variant.

The Joint Committee on Vaccination and Immunisation (JCVI) is now advising that all adults aged 18 to 39 should be offered a booster dose to increase protection. Those aged 40 and over are already eligible for a booster vaccine.

Booster doses should be given no sooner than three months after people have had their second dose of an original vaccine – shaving three months off the current six-month wait, according to the JCVI.

In further advice, young people aged 12 to 15 should be offered a second dose of the Pfizer/BioNTech Covid-19 vaccine, no sooner than 12 weeks after their first dose.

The JCVI also said that severely immunosuppressed people should be offered a booster dose no sooner than three months after completing their primary course of three doses.

“If you are eligible for a booster, please take up the offer and keep yourself protected as we head into winter...”

There have now been five confirmed cases in England and six confirmed cases in Scotland. Confirmed cases have been reported in many countries, including across Europe.

Professor Wei Shen Lim, chair of the JCVI said: “Having a booster dose of the vaccine will help to increase our level of protection against the Omicron variant.

“This is an important way for us to reduce the impact of this variant on our lives, especially in the coming months.

“If you are eligible for a booster, please take up the offer and keep yourself protected as we head into winter.”

When asked at a public health press conference today whether there was any change in its advice for pregnant women, he replied "all the advice we prescribe applies to pregnant women".

He added: "Lets not wait any further before opening a booster programme for young adults lets bring younger adults into the booster programme now so that any drop in vaccine protection they may get will be mitigated."

"With regards to speed of advice there is a time to move quickly and their is a time to move more cautiously."

Where circumstances change the physicist said this would necessitate making decisions "more quickly" but there was no hard and fast approach.

"Going quickly all the time isn't always the best and going slowly all the time isn't always the best either," he said.

"Given there is always uncertainty and we are trying to keep abreast of the data as much as possible."

The JCVI said that both the Moderna and Pfizer/BioNTech vaccines can be given as a booster for adults – with equal preference given to both.

Experts believe the new Omicron variant, which is believed to have first emerged in South Africa, could reduce the effectiveness of vaccines in stopping people getting infected – although they think vaccines may still protect against severe disease.

However, it could be three more weeks before further details emerge from scientists on how transmissible the variant is, whether it evades vaccine protection and whether it causes more severe disease.

In the meantime, Health Secretary Sajid Javid asked people to "remain vigilant" and told parliament this afternoon "our vaccines remain our best line of defence" against the virus.

He added there is a "lot we don't know" about the new variant still but it remained important "we get as many jabs in arms as possible."

The government minister said: "We are taking a well rounded view looking not just the impact of these measures but the impact to the economy, education and non Covid-health such as mental health."

"We always knew there would be bumps on the road but this is not a time to waiver this is as time to b e vigilant and getting there jab when the time comes, following the rules we put in place and getting tested regularly and protect the progress we have made."

Priority will be given to older adults and more vulnerable adults.

Severely immunosuppressed people should also be be offered a booster dose no sooner than three months after completing their primary course of three doses.

From tomorrow, the wearing of face masks is set to be compulsory in shops and on public transport, while PCR tests will be brought back in for travellers returning to the UK.