Boris Johnson has explained what needs to happen over the coming weeks for lockdown to be lifted.
The Prime Minister said the government would not rush into removing restrictions for fear the virus could tear through younger people more rampantly.
Speaking at a Downing Street briefing on Friday, Mr Johnson said that once the most vulnerable have been vaccinated by mid-February "we will think about what steps we could take to lift the restrictions".
He added: "What we can't have is any false sense of security so that we, as it were, lift the restrictions altogether and then the disease really runs riot in the younger generations."
The Prime Minister said around one third of Covid patients admitted to hospital are under 65, while a quarter are under 55.
He said: "So it can affect and does affect huge numbers of younger people as well, often very badly, and the risk is that those numbers would be greatly inflated if we let go too soon in circumstances where the disease was really rampant.
"That is not to say that I don't want to try to get to relaxations as soon as we reasonably can - but there are a lot of things that have to go right."
The PM said he wants to get to a stage where they are confident they have vaccinated enough people - those in care homes, those over 80, 70 and others - and then depending on the effectiveness of that, the Government will think about what steps to take.
Mr Johnson refused to commit to a date when the national lockdown will be lifted.
The current nationwide lockdown is set to last until February 15, with the measures set to be reviewed around this date.
The PM said 'we can't have any false sense of security' in case the virus 'runs riot' among the younger generations.
He said: "That's not to say I don't want to try to get to relaxations as soon as we reasonably can but there's a lot of things that have to go right.
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"We have to make sure the vaccine programme is working well, we have to make sure that there are no new variants or no big changes in our understanding of the disease and we've got to work together to deliver the results of the current lockdown and get this disease under control.
"There are some signs in some places that that's working but it's going to take a huge national effort."
Chief medical officer Professor Chris Whitty said the coronavirus restrictions would need to be lifted gradually.
He added: ''We're not going to move from a sudden lockdown situation to nothing.
"It will have to be walking backwards by degrees, testing what works, and then if that works going the next step.''
