The UK Covid alert level has been raised following a rapid increase in omicron cases being recorded.
Following advice from the country's four chief medical officers and NHS England's national medical director, the UK coronavirus threat level was raised from Level 3 to Level 4 on Sunday, December 12.
On Wednesday, December 15 the Prime Minister addressed Britons in a Covid press conference to praise the "great national fight-back" that has followed the Government's Omicron Emergency Boost drive, a vaccination drive to get all adults boosted before the new year.
Boris Johnson revealed that more than 20,000 volunteers have signed up as vaccination stewards since Sunday night as part of a "territorial army" in what he called "a race against time to get those jabs in arms".
He urged viewers to "do something this Christmas you can tell your grandchildren about many years from now."
Why have we moved to Level 4?
The decision to increase the alert level followed advice from the UK Health Security Agency (UKHSA) after a further 1,576 confirmed cases of the omicron mutation were recorded in the UK as of Monday, Dec. 13.
The first death from the variant in the UK has also been recorded.
As of Wednesday, Dec. 15, the total number of confirmed UK omicron cases has since surpassed 10,000, according to the latest data
The UK recorded its highest ever daily Covid cases since the pandemic began with official figures reporting 78,610 on Dec. 15 too.
Chris Whitty, England's Chief Medical Officer, warned during the conference that "we have to be realistic that records will be broken a lot over the next few weeks as the rates continue to go up."
Increasing the UK Covid alert level to Level 4 means the epidemic is "in general circulation, transmission is high and direct Covid-19 pressure on healthcare services is widespread and substantial or rising", according to government guidance.
In a joint statement, the CMOs and NHS England's Professor Stephen Powis said the emergence of omicron "adds additional and rapidly increasing risk to the public and healthcare services".
They added: "Early evidence shows that omicron is spreading much faster than delta and that vaccine protection against symptomatic disease from omicron is reduced.
"Data on severity will become clearer over the coming weeks but hospitalisations from omicron are already occurring and these are likely to increase rapidly."
The five officials, including England's CMO Professor Chris Whitty, Northern Ireland's Sir Michael McBride, Scotland's Professor Gregor Smith, and Wales' Dr Frank Atherton, said the NHS was already under pressure "mainly driven by non-Covid pressures", with omicron's ability to escape vaccines "likely" to add to those demands.
"It is extremely important that if you are eligible, you get your Covid vaccination now - whether this be your first, second or booster dose," they said.
"People should continue to take sensible precautions including ventilating rooms, using face coverings, testing regularly and isolating when symptomatic."
Will this mean more restrictions?
The increased Covid alert level comes amid warnings that more restrictions may be needed to tackle omicron, with the UK facing an "inevitable" large wave of infections.
That is according to Dr Susan Hopkins, the chief medical adviser for the UKHSA, who said people will have to reduce social contact as much as possible, with omicron cases being detected among hospital patients.
Dr Hopkins said more measures may be needed, adding that the Government has "very difficult" decisions ahead, even after triggering its winter Plan B proposals, which include introducing Covid passports for large venues.
"I think that the restrictions that the Government announced are sensible. I think that we may need to go beyond them. But we'll need to watch carefully what happens with hospitalisations," she told the BBC.
When was the last time the UK was in Level 4?
The last time the alert level was Level 4 was in February, when on February 25 the alert level was downgraded from Level 5 to Level 4.
During that time, the restrictions were as follows:
Primary and secondary schools were closed Indoor hospitality and non-essential retail, such as hairdressers and clothes shops, were closed Entertainment venues, such as cinemas, zoos and theme parks, were closed "Stay At Home" order was in-place Organised outdoor sport was banned Mixing between households was prohibited Hugs were banned
However, no further restrictions than those currently imposed by Plan B have been announced.
How does the UK alert level system work?
The Government first unveiled the alert level system in May 2020, with the Joint Biosecurity Centre (JBC) now responsible for calculating changes in the level to help "communicate the current level of risk clearly to the public".
The five-tier system, which has been designed to mirror the UK's independent terror alert system, is also colour-coded, ranging from green to red.
The levels are:
Level 1 (green): Covid-19 is not known to be present in the UK Level 2: Covid-19 is present in the UK, but the number of cases and transmission is low Level 3: a Covid-19 epidemic is in general circulation Level 4: a Covid-19 epidemic is in general circulation; transmission is high or rising exponentially Level 5 (red): as level 4 but there is a "material risk of healthcare services being overwhelmed"
This article is being kept updated with the latest news and government guidance daily.