Boris Johnson has been accused of allowing the UK to enter the "darkest moment of the pandemic" by delaying decisions at key moments of the coronavirus crisis.
Sir Keir Starmer said Covid-19 is "out of control" and the UK is in a "very serious" situation, as he levelled the blame at the prime minister.
Speaking ahead of a vote on England's lockdown, the Labour leader said the NHS being "under huge strain" is "not just bad luck, it's not inevitable, it follows a pattern".
He accused the PM of failing to learn lessons from the first wave of the virus, during which "the government was repeatedly too slow to act".
Sir Keir said the UK ended 2020 with "one of highest deaths tolls in Europe and the worst-hit economy of major economies" because the PM delayed decisions, despite warnings and advice by scientists.
He cited a number of times warnings were given, but decisions were not made for weeks.
A circuit break lockdown was recommended by the Scientific Advisory Group for Emergencies (SAGE) in September, Sir Keir said, but the prime minister "delayed for weeks" the November lockdown that followed.
He said the the most recent advice about the current situation was given on December 22, "but no action was taken for two weeks ".
Sir Keir said: "We had a tiered system that didn't work and then we had the debacle of the delayed decision to change the rules on mixing at Christmas. "
He added: "These are the decisions that have led us to the position we're now in - and the vaccine is now the only way out and we must all support the national effort to get it rolled out as quickly as possible."
The Labour leader said that his party will support the new restrictions and urged people to comply with them.
The prime minister thanked Sir Keir for his party's support in the Commons vote, which is expected at 7pm, but defended his response to the virus, saying many points made by the Labour leader were "political" ones.
He hit back at Sir Keir, saying he previously acted with "derision" about the vaccination programme.
He told the Commons: "I must say I do remember the derision with which he attacked the vaccine taskforce and the efforts that they went to to secure huge... supplies. I remember it well, it was at Prime Minister's Question Time. "
Mr Johnson said the government will use "every available second" during the lockdown to place an "invisible shield" around elderly and vulnerable people, via the Covid-19 vaccine.
He said the gradual end of lockdown may begin after the February half term, but people "should remain extremely cautious about the timetable ahead".
"Emergence from the lockdown cocoon will not be a big bang but a gradual unwrapping," he added.
He insisted "schools are safe" and the "most dangerous part of going to school, even in the midst of a global pandemic, remains crossing the road in order to get there".
But he said he had been forced to close schools during lockdown to stop pupils being a "vector" for infecting family members at home and promised that schools would be the first to reopen when lockdown begins to lift.
The PM said "there's a fundamental difference between the regulations before the House today and the position we faced at any previous stage, because we now have the vaccines that are our means of escape.
"And we will use every available second of the lockdown to place this invisible shield around the elderly and the vulnerable."
Labour's shadow health secretary Jonathan Ashworth said the Prime Minister has been "short of judgment" and should have put England into lockdown sooner.
He told the Commons: "We should have locked down sooner. We are voting this lockdown through on the twelfth night, yet in the run-up to Christmas the alarm bells should have been ringing."
He added: "This is a national tragedy and why is it this Prime Minister, with all the scientific expertise at his disposal, all the power to make a difference, always seems to be last to grasp what is needed to happen?
"The Prime Minister hasn't been short of data, he has been short of judgment and yet again we are all paying the price."
Mr Ashworth called for the Government to ramp up its vaccination programme to six million doses a week.
He said: "Two million a week would be fantastic but it should be the limit of our ambitions, we should be aiming to scale up to three, then five, then six million jabs a week over the coming months."