All people aged 18 and over are to be offered a Covid-19 booster vaccine as part of efforts to tackle the spread of the new Omicron variant.

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, in order of descending age groups, to increase their level of protection. Those aged 40 and over are already eligible for a booster vaccine.

Read more: Does the Covid vaccine work against Omicron variant? What we know so far

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.

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.”

Which jabs can be given as a booster?

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 could reduce the effectiveness of vaccines in stopping people getting infected, though 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 a speech to the King’s Fund annual conference on Monday, Amanda Pritchard, chief executive of the NHS in England, said NHS staff will “move heaven and earth to vaccinate as many people as possible” to ensure that people can enjoy Christmas with their loved ones.

But she said volunteers are needed to help the “vital national effort” of expanding the coronavirus vaccine programme, adding the service “will not be able to do it alone”.

Dr June Raine, chief executive of the Medicines and Healthcare products Regulatory Agency (MHRA), said: “The public can be confident that our robust regulatory assessment supports the JCVI’s recommended extension to the vaccination campaign.

“This further strengthens our ability to ensure people are protected against Covid-19 and saves lives.

“Our safety monitoring to date shows that Covid-19 vaccines continue to have a positive safety profile for the majority of people.

“When you are called for your booster dose, you can come forward confident that the benefits in preventing serious Covid-19 far outweigh any risks.”

What do we know about the Omicron variant

On Monday afternoon, health ministers from the G7 group of nations held an urgent meeting to discuss the impact of the new Omicron variant.

According to the World Health Organisation (WHO), preliminary evidence suggests Omicron carries a higher risk of reinfection.

The UK Health Security Agency (UKHSA) had identified five cases of the Omicron Covid-19 variant in England as of Monday evening, bringing the total to five.

Three were in London - Westminster, Camden, and Wandsworth, with the others in Brentwood, Essex, and Nottingham.

All are linked to travel to southern Africa.

UKHSA chief executive Dr Jenny Harries said: “It is very likely that we will find more cases over the coming days as we are seeing in other countries globally and as we increase case detection through focused contact tracing.

"That’s why it’s critical that anyone with Covid-19 symptoms isolates and gets a PCR test immediately.”

From Tuesday, 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.