All adults will be offered Covid booster jabs, as part of measures to protect the UK from a potential wave of cases driven by the new Omicron variant.

The Joint Committee on Vaccination and Immunisation (JCVI) has also said that the minimum gap between the second dose and booster should be reduced to three months.

There are fears that the new strain, which was first found in South Africa, could be more infectious than previous forms of the virus.

There are also concerns it may be more resistant to the vaccines already in use. But experts have stressed that jabs will still offer some protection and remain the best line of defence against Covid.

So far around a dozen Omicron cases have been confirmed in the UK. Six of them are in Scotland, with others Chelmsford in Essex, Nottingham and London.

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Jabs have previously been offered to everyone over 40 along with vulnerable groups, with five walk-in centres now operating in Norfolk.

Some 268,000 eligible people have so far been given the injection in Norfolk and Waveney.

Now the JCVI says all over-18s should be offered the jab, while the interval between second dose and booster should be cut from six to three months.

That means millions more people will be eligible for a booster jab across the UK.

At a briefing on Monday afternoon England's deputy chief medical officer Jonathan Van-Tam said the NHS would announce over the coming days how it will "operationalise" the call to speed up booster jabs.

Prof Van-Tam said the NHS will deliver the booster campaign in an "orderly" way to avoid younger people jumping ahead of those who are more vulnerable.

"The important message that the NHS wanted me to convey to you today is that they understand the real urgency of this," England's chief medical officer said.

"They are up for the task but they say that they will contact you when you need to act and they will open the booking in an orderly way."

Prof 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."

Children aged 12 - 15 should also be invited for their second dose three months after their first, the JCVI says.

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Cath Byford, chief nurse with the NHS Norfolk and Waveney Clinical Commissioning Group, said: “The vast majority of those being hospitalised with serious illness from Covid-19 are those who have not been vaccinated. We strongly encourage everyone who is eligible to arrange their vaccine or booster dose now.

“Vaccines are the best way to protect yourselves and your loved ones and reducing Covid-related hospital admissions will help the NHS cope better during the winter months and reduce disruption to routine and planned care.”

Meanwhile, masks will become compulsory again on public transport and in shops from 4am on Tuesday.

Teachers and pupils in Year 7 and above are now being "strongly advised" to wear them in communal areas outside classrooms in England.

But the government has stopped short of telling schools to cancel nativity plays, saying the decision lies with individual heads.

Norfolk County Council said: "We have been working closely with headteachers throughout the pandemic, offering guidance and support with managing Covid and we continue to do so."

Dr Jenny Harries, the chief executive of the UK Health Security Agency, acknowledged it was "very likely" that further cases of Omicron would be discovered in the coming days.

But health secretary Sajid Javid told families they should plan for a "great" Christmas "as normal" and insisted it was "nowhere near" time to reintroduce social distancing rules and work-from-home guidance.

In a speech to the annual conference of health think tank the King's Fund 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".

Where can you get a booster jab?

There are five walk-in vaccine centres in Norfolk:

Paddock Road Surgery, Paddock Road, Harleston IP20 9AT

Connaught Hall, Station Rd, Attleborough NR17 2AS

Shakespeare Barn, King's Lynn Arts Centre, King Street, Kings Lynn PE30 1HA

Castle Quarter Shopping Centre, 100 Castle Meadow, Norwich NR1 3DD

Beetley Ward, Dereham Hospital, Northgate, Dereham NR19 2EX (open Thursdays, Fridays, Saturdays and Sundays only).

Anyone registered with a GP can book a jab via the NHS website.