The UK Covid Alert Level has been increased from Level 3 to Level 4 “in light of the rapid increase in Omicron cases”, the four UK chief medical officers said in a joint statement.

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 the statement, the four UK chief medical officers and the NHS England national medical director said the emergence of Omicron “adds additional and rapidly increasing risk to the public and healthcare services”.

The statement said: “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.”

They added: “The NHS is currently under pressure mainly driven by non-Covid pressures. With a variant spreading with increased transmissibility and reduced vaccine effectiveness, we are likely to see this pressure rise soon. It is extremely important that if you are eligible, you get your Covid vaccination now – whether this be your first, second or booster dose.

“People should continue take sensible precautions including ventilating rooms, using face coverings, testing regularly and isolating when symptomatic.”

The news comes after a total of 51,254,510 first doses of Covid-19 vaccine had been delivered in the UK by December 11, Government figures show.

This is a rise of 25,378 on the previous day.

Some 46,742,069 second doses have been delivered, an increase of 36,873.

A combined total of 23,124,829 booster and third doses have also been given, a day-on-day rise of 530,086.

Separate totals for booster and third doses are not available.