Lockdown measures will remain in place until at least March 8, Boris Johnson said as he earmarked that date to begin the reopening of England's schools.
The Prime Minister confirmed that hopes of all pupils returning to class after the February half-term have been abandoned as the battle with coronavirus remained "perilous".
Government figures showed a further 1,725 people had died within 28 days of testing positive for Covid-19 as of Wednesday, bringing the UK total to 101,887, while there were a further 25,308 lab-confirmed cases.
The March reopening target is based on progress in vaccinating the most vulnerable groups in society by mid-February and then giving the jab time to take effect.
So far 7,164,387 people have received a first dose of either the Pfizer or AstraZeneca vaccines – a rise of 311,060 on the previous day's figures – although Mr Johnson acknowledged a "sense of frustration" about the patchy nature of the rollout.
Based on the latest figures, an average of 412,401 first doses of vaccine would be needed each day in order to meet the Government's target of 15 million first doses by February 15.
The Government will publish a strategy for the "gradual and phased" easing of lockdown in the week beginning February 22, with schools expected to be the first to reopen.
England's schools are currently closed to all but vulnerable pupils and the children of key workers.
The Prime Minister told MPs: "The first sign of normality beginning to return should be pupils going back to their classrooms."
Arrangements to provide free school meals for eligible pupils would be extended and an extra £300 million will be available for tutoring to help children catch up on missed lessons.
At a Downing Street press conference Mr Johnson said: "When we look at the toll of this pandemic it must be measured not only in the tragic loss of life that we've endured, with over 100,000 deaths.
"But I'm afraid we must also remember not just the damage to the economy but the lost weeks and month of education and the real risk of damage to the prospects of our young people."
Schools will only reopen if the Government can be confident it will not result in a "huge surge" in cases.
The plan will also depend on evidence showing the effectiveness of the vaccines in preventing death and serious illness.
He said the road map being published in February will set out a plan to "get our lives back to as close to normal as possible".
But he warned it was a timetable that is "inevitably going to be subject to adjustment".
The Government's chief scientific adviser Sir Patrick Vallance said: "We are at a position where the lockdowns have worked, they've slowed this down, they've reached a position where it has reached a plateau and is beginning to decline – and we see that in cases, we're beginning to see that in hospital admissions and we're beginning to see that in deaths – but it is early days.
"This isn't coming down quickly, we remain at very high levels and it is going to take weeks for this to come down to really low levels."
The Government has warned that the emergence of a vaccine-resistant new variant could derail its strategy and Mr Johnson and Home Secretary Priti Patel set out plans for tougher controls on international travel to reduce the risk of importing mutant strains.
The measures include a 10-day quarantine in hotel for travellers from 30 high-risk countries which are currently subject to travel bans including South Africa, Portugal and many South American nations.
UK nationals and residents who cannot be refused entry when returning home "will be met at the airport and transported directly into quarantine", Mr Johnson said.
Similar measures are expected across the UK, although Scotland and Wales have both indicated they could go further than Mr Johnson's plan for England.
People wishing to travel abroad will also be required to make a declaration stating why they need to make the journey, which will be checked by carriers prior to departure.
In other developments:
– Dr Richard Harling, director of health and care at Staffordshire County Council, said local authorities will be dealing with the virus "throughout the 2020s, into the 2030s".
– The row between the European Union and AstraZeneca escalated, with Brussels claiming it had a contractual right to vaccines manufactured in the pharmaceutical giant's UK plants in order to meet demand in the bloc.
We can confirm that the investigation of the suspicious package today has been concluded. The package was made safe and staff are now being allowed back into the facility.
We are grateful to the authorities and experts for their swift response and resolution of the incident.
— WockhardtUK (@WockhardtUk) January 27, 2021
– Production at the Wockhardt site in Wrexham, which provides fill-and-finish services for the AstraZeneca vaccine, was paused while the police and army investigated a suspect package.
The current phase of the vaccination programme covers the top four priority groups, including people aged over 70, care home residents and frontline health and care workers, around 15 million people.
Mr Johnson said the Government was on target to meet the goal of offering them a first dose by February 15 "if we can get the supplies" of vaccine.
Labour leader Sir Keir Starmer called for teachers and key workers to be vaccinated once the four top priority groups defined by the Joint Committee on Vaccination and Immunisation (JCVI) had received the jab.
Under the existing plan, the JCVI's next priority groups include all over-50s and people with underlying health conditions.
Mr Johnson said the JCVI list was designed to prioritise those most likely to die or suffer from coronavirus and Sir Keir "has to explain which vaccines he would take from which vulnerable groups" to give to key workers.