The UK's coronavirus alert level has been raised from three to four due to the rapid spread of Omicron.
Level four means a high or rising level of transmission, and pressure on healthcare services is rising.
"No one should be in any doubt, there is a tidal wave of Omicron coming," British Prime Minister Boris Johnson said in a TV statement on Sunday evening.
A new target has been set to give boosters to all adults who want one by the end of the month, he said.
Johnson gave his update on Sunday evening - just hours after the UK's Covid alert level was raised to four due to the spread of the new Omicron virus variant.
"It is now clear that two doses of vaccine are simply not enough to give the level of protection we all need," Johnson added.
Britain is one of the most affected countries by the Corona pandemic, as it has recorded more than 10.5 million cases, as well as more than 146,000 deaths since the outbreak began in March last year.
