All people aged 18 and over will be offered a Covid-19 booster jab as the government steps up efforts to tackle the new Omicron variant.

Health secretary Sajid Javid said five cases of the new variant of concern have now been identified in the England, along with six in Scotland.

He said: "We expect cases to rise over the coming days.

“The new variant has also been spreading across the world. Confirmed cases have been reported in many countries, including Austria, Belgium, the Czech Republic, Denmark, Germany, Italy, the Netherlands and Portugal.

“In this race between the vaccines and the virus, the new variant may have given the virus extra legs.”

Millions more people will become eligible for the third shot of the vaccine after initial evidence suggested that higher antibody levels may protect better against the variant.

Health experts at the Joint Committee on Vaccination and Immunisation (JCVI) are 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.

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.”

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.”

On Monday afternoon, health ministers from the G7 group of nations are holding 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 now has nine confirmed cases of the variant after the Scottish government announced on Monday morning it had discovered four cases in Lanarkshire and two in the Greater Glasgow and Clyde area.

One other case has been identified in Brentwood, Essex, with another in Nottingham, while a third case was detected in England on Sunday in a person with travel links to southern Africa who visited Westminster before leaving the country.

Scotland’s Deputy First Minister John Swinney said that some of the Omicron variant cases identified in Scotland have no travel history, which suggests there is a degree of community transmission.

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.