The next phase of the Covid vaccine programme will begin, after more than 15 million people across the UK received their first dose of a vaccine.
The first four priority groups have been vaccinated - paving the way for the next phase of the the rollout – covering the next five priority groups, including the over 50s - to start.
Prime Minister Boris Johnson hailed the the achievement – just over two months after the vaccination programme delivered its first jab – as a “significant milestone” in the fight against the disease.
The PM confirmed on Sunday that it had been met in England after First Minister Mark Drakeford announced on Friday that Wales had become the first of the four nations to reach it.
Anyone in the top four priority groups who has not yet been offered a vaccine is being encouraged to contact the NHS to book an appointment for a jab.
Ministers are to begin reviewing coronavirus lockdown restrictions in England, a week to the day when Mr Johnson will outline his "roadmap" out of lockdown on February 22.
Health Secretary Matt Hancock revealed very little when asked whether some restrictions would be lifted now the first vaccine target had been reached.
He told ITV News "the vaccine is the route out of this pandemic", adding: "The PM will set out the timing of the roadmap and the sorts of decisions we're able to make to release lockdown, we'll set that next Monday.
"The work we'll be doing this week is to make the judgements about what we can do to exit lockdown safely, yet quickly.
"That is the difficult balance, we want a sustainable exit so we don't have to go back into lockdown."
Scientists have warned that lessons must be learned from the “mistakes” made previously in relaxing lockdown measures too fast.
Professor Neil Ferguson, who advises the Government as part of the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), warned that more information is needed about how effective vaccines are going to be.
He told Good Morning Britain: “We have results from scientific studies, clinical trials, but the real world is a different thing and so, again as the Government has said, we need to see how much protection vaccinated people have, how quickly death rates come down before we can be completely confident about going that next step and really reopening.”
The scientist said he feels it is “quite likely” that all schools in England will reopen on March 8 but said there will then need to be two or three weeks to look at how that affects case numbers.
He said: “The modelling we and other groups and universities in the UK have been doing would suggest there probably is leeway to reopen all schools.
“But of course that poses slightly more of a risk than just, for instance, reopening primary schools.”
Meanwhile, strict new quarantine rules are coming into force requiring UK nationals returning from 33 “red list” countries to isolate in a Government-designated hotel for 10 days in an attempt to prevent new strains of the virus entering the country.
NHS England has already sent out 1.2 million invitations to the over 65s to book an appointment, with a similar number expected to go out this week.
The government is aiming to get an offer of a vaccine to the estimated 17 million people in the next five groups by the end of April.
In a video message posted online on Sunday, Mr Johnson said there was still “a long way to go” and that there would “undoubtedly be bumps in the road”.
The PM will this week begin considering how restrictions in England may be eased ahead of his February 22 statement.
He is already under pressure from some Tory MPs to push ahead amid frustration at the damage that is being done to the economy and the impact on people’s lives.
More than 60 lockdown-sceptics in the Covid Research Group (CRG) signed a letter calling for him to commit to a firm timetable, starting with the re-opening of schools on March 8 and ending with the lifting of all legal controls by the end of April.
Ministers however remain more cautious. Mr Johnson said they would need to study the data “very, very hard” for evidence that the rollout of the vaccines is driving down the incidence of the disease, as the numbers of cases fell.
While he was “optimistic” that a “cautious” easing of lockdown measures would be possible, he said that he did not want to be forced into a “reverse ferret” if there was a fresh resurgence of the disease.
Health Secretary Matt Hancock has previously said they needed to have “broken the link” between case numbers and hospitalisations and deaths as more and more people received the protection of the vaccine.
Scientists have warned of a new wave of the pandemic as big as the current one if measures are relaxed too quickly while senior NHS figures say the health service remains under intense pressure.
Chris Hopson, the chief executive of NHS Providers, warned against easing restrictions “prematurely” saying they needed to remain vigilant for new variants of the virus which may prove less susceptible to the vaccines.
“We must not let down our guard in our fight against the virus. There is still a lot to understand before we can be wholly certain of the impact of the vaccination programme,” he said.
Minister have said the re-opening of schools in England on March 8 remains their first priority, although reports have suggested the return may be staggered, with secondary schools going back a week later.
Foreign Secretary Dominic Raab said on Sunday that they were confident they could “start the process” of schools re-opening on that date.
After schools, it is expected the next areas of easing will be non-essential shops and the rules on outdoor recreation and socialising.
The hospitality sector and the CRG meanwhile are pressing for pubs and restaurants to re-open in time for the Easter weekend at the beginning of April.