Boris Johnson has urged the two million people in the top four most “at-risk” groups who are yet to be inoculated to take up the offer of a Covid vaccine.
The prime minister also announced that ministers hope that everyone in the first nine priority groups will have received a jab by the end of April.
He told a Downing Street press conference: "There's no doubt we've made great strides, with just over 13 million people now vaccinated in our United Kingdom, including one in four adults in England, over 90 per cent of everyone over 75 and over 90 per cent of eligible residents of care homes for the elderly.
“But that still leaves nearly two million people, a population roughly twice the size of Birmingham, that we still hope to reach. Now is the moment to do it.”
He issued a particular call to social care workers who still have not been vaccinated to contact their employer to “fix it up”.
There have been suggestions of low take-up rates among some working in care homes.
He said he was urging the two million to come forward now to help the UK progress on the “long and hard road back to normality”.
Ministers have set a target to inoculate all those in the first four groups by Monday.
But the prime minister said: “The reason I make this appeal today for people to come forward in those groups to get vaccinated is not to hit some numerical target but to save lives, prevent serious illness and so the whole country can take another step on the long and hard road back to normality.”
Ministers admit that higher than expected numbers have come forward to be vaccinated.
Mr Johnson also welcomed the World Health Organisation's support for his government's strategy to delay the second dose of the Oxford/AstraZeneca vaccine.
The UK made the decision not to give two doses within three weeks, in a bid to maximise the number of people who received protection from their first jab.
But a number of other governments rejected that approach and stuck with the three-week timetable.
Mr Johnson said: "It was good to see the World Health Organisation today confirm its support for the Oxford/AstraZeneca vaccine for use in everyone over the age of 18 and obviously everyone over 65 and also supporting the 12-week interval between the two doses.
"Indeed they say the longer interval provides greater protection."
Mr Johnson urged people to be “a little bit more patient” on whether they can book summer holidays.
The prime minister told the Downing Street press conference: “I’m afraid it is just too early for people to be certain about what we will be able to do this summer. We hope to be able to say more in the week of the 22nd (February).
“I understand why people want to make plans now but we’re just going to have to be a little bit more patient.”
Mr Johnson said Public Health England figures showing a reduction in Covid-19 cases did not necessarily reflect the success of the vaccination campaign.
“I’ve looked at the data and scrutinised it with my layman’s eye and so far, yes we are getting the numbers down,” he said. “But can I see results that I think are directly attributable to the vaccine? Although I’m assured that will happen soon, I can’t say that I can see them yet.”
On lifting lockdown measures, Sir Patrick Vallance said it would be done with “caution” and based on the data.
He said there were still a “significant number of people in high-risk groups” who had not been vaccinated.
Sir Patrick said: “Those people remain at risk and so it’s important we go cautiously in opening up, in order to be able to measure the effects.”
He added: “The virus isn’t going to be particularly interested in dates.”
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