The announcement that UK regulators had become the first in the world to authorise the breakthrough Pfizer/BioNTech inoculation for use was greeted with joy and relief across the country, following nine months of lockdowns and restrictions and around 60,000 deaths.
But Mr Johnson warned that “this is not over” as he pleaded for people to stick with the tough three-tier system of regional restrictions which came into effect across England the same day.
On the day clearance for vaccinations was granted, figures showed 16,170 daily confirmed cases of Covid-19 and 648 fatalities, bringing the official death toll to 59,699.
Jonathan Van-Tam, the deputy chief medical officer, warned of a “tidal wave” of new infections which would knock back the process of eradicating the threat from Covid-19 if people abandoned social distancing and controls on economic activity.
Watch: Professor Jonathan Van-Tam urges public to take vaccine if they want to see normal life to return
And as the government prepared to combat “anti-vaxxer” messages rejecting immunisation, Prof Van-Tam said that refusing the jab would only delay the day when pubs, restaurants, concert halls, sports stadiums and theatres can fully reopen and friends and families can meet again.
The prime minister told a Downing Street press conference that the certification of the jab as safe and effective gave “sure and certain knowledge that we will succeed and together reclaim our lives and all the things about our lives that we love”.
But he warned: “It will inevitably take some months before all the most vulnerable are protected – long, cold months.
“So it’s all the more vital that as we celebrate this scientific achievement we are not carried away with over-optimism or fall into the naive belief that the struggle is over.”
Mr Johnson revealed that it will not initially be possible to deliver supplies of the Pfizer jab to care homes, despite their residents and staff being top of the list of priorities for immunisation.
Further approvals will be needed from the Medicines and Healthcare products Regulatory Agency (MHRA) before the 975-dose cases in which the product is shipped from Belgium can be broken down into small enough batches for distribution to homes while keeping them below the -70C temperature above which they become ineffective.
Instead, jabs will be administered first in 53 hospitals across England from next week to over-80s, care home staff and NHS workers, who have all been identified as priority at-risk people.
Later in the month, the operation will be extended to groups of GP practices coming together in 1,000 local vaccination centres across England.
But with only 800,000 doses expected to be delivered before Christmas and each patient needing two shots, three weeks apart, the vast majority of the country will have to get through the festive season before being offered any protection.
It will not be until March or April that the first phase of vaccination – covering all over-50s, health and care workers and people whose health conditions put them at risk – can be expected to be complete, said NHS England chief executive, Sir Simon Stevens.
Prof Van-Tam said: “If we relax too soon, if we just, kind of, go ‘Oh, the vaccine’s here, let’s abandon caution’, all you are going to do is create a tidal wave of infections,” he warned.
“And this vaccine has then got to work in a headwind to get back ahead of the game. And that will make it harder.”
Urging people to stick to the regional restrictions which have seen 99 per cent of England subjected to tough controls on socialising, Mr Johnson warned: “The worst things now would be to think that this is the moment that we can relax our guard and think that it’s ‘game over’ in the fight against Covid.”
He said: “It would be a really fatal mistake now to respond to this good news by letting the virus run riot again, letting it get out of control by too much transmission over Christmas.
“That’s why we have to stick very tightly to the tiers that we have set out.”
Prof Van-Tam sent a message to opponents of vaccination, many of whom are also prominent in protests against lockdown restrictions.
“Everyone wants social distancing to come to an end – we are fed up with it,” he said.
“Nobody wants lockdowns and to see the damage they do. But if you want that dream to come true as quickly as it can come true, then you have to take the vaccine when it is offered to you.
“Low uptake will almost certainly make restrictions last longer.”
The deputy chief medical officer said it was unlikely that Covid-19 would be entirely eradicated, predicting that it may become a seasonal problem on a similar scale to winter flu and that Britons may voluntarily continue the use of hand sanitisers and face coverings which have become second nature over the past nine months.
“Do I think there will come a big moment where we have a massive party and throw our masks and hand sanitiser and say ‘that’s it, it’s behind us’, like the end of the war? No, I don’t,” he said.
“I think those kind of habits that we have learned … will, perhaps persist for many years. And that may be a good thing if they do.”
Apparently somewhat alarmed by the suggestion that crisis conditions may persist for years, Mr Johnson responded: “Maybe, on the other hand, we may want to get back to life pretty much close to normal.”
Watch: All you need to know from the Government's coronavirus briefing
Labour leader Keir Starmer offered the services of his frontbench team to help the government demonstrate cross-party consensus on the need to get the UK vaccinated.
“This rollout is one of the biggest logistical exercises since the Second World War,” said Sir Keir. “We need the best of Britain, we need parties pulling together and I’m very happy to put my party behind that effort.”