England's Chief Medical Officer told the coronavirus briefing on Wednesday that the Omicron coronavirus variant was spreading rapidly at the same time as the Dela variant remained in circulation. Prof Whitty stressed the importance of speed with the rollout of the booster programme to improve immunity from the new strain. He warned that with rising cases a number of Covid records would be broken in the coming weeks.
Prof Whitty told the press conference: "What we've got is two epidemics on top of one another.
"An existing Delta epidemic, roughly flat, and a very rapidly-growing Omicron epidemic on top of it."
He warned: "This is a really serious threat at the moment. The how big a threat - there are several things we don't know, but all the things that we do know, are bad.
"And the principle one being the speed at which this is moving, it is moving at an absolutely phenomenal pace."
Prof Whitty warned that Omicron posed a really serious threat and that what health officials already knew about was "bad".
He said: "This is a really serious threat at the moment. The how big a threat - there are several things we don't know, but all the things that we do know, are bad.
"And the principle one being the speed at which this is moving, it is moving at an absolutely phenomenal pace."
He added: "We do have some things going for us this time of which the most important is the existence of effective vaccines and the ability to boost at speed at this stage."
He insisted the Government's Plan B was the right thing to do, adding that boosters also "provide an excellent level of protection".
He added: "We think that, given the balance of risks and the balance of continuing uncertainties about Omicron, this is the right approach to take.. to do these things at once.
"The progress we are making with the booster is vital... we really are boosting huge numbers of people now."
He said over 90 percent of people aged 75 to 79-year-olds had been given a booster, adding it was those groups that "provide the bulk of those who are sadly going to die from Covid".
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Earlier he said: "While hospital admissions are going up nationwide, we're starting to see admissions coming down among some of the more vulnerable older age groups where we've already got those boosters in arms."
He added: "People have responded with an amazing spirit of duty and obligation to others and I want to say that each and every one of you who rolls up your sleeve to get jabbed is helping this national effort."
Prof Whitty said it is sensible to prioritise the social interactions that matter, especially in the run-up to Christmas.
He said: "I think that what most people are doing is, and I would think this seems very sensible, is prioritising the social interactions that really matter to them and, to protect those ones, de-prioritising ones that matter much less to them."