Considering it was such a big deal, there was - somewhat surprisingly - no gloating or triumphalism from Boris Johnson at his latest Downing Street news conference.
© ImagebridgeBoris Johnson said it was 'no moment to relax' after reaching the first vaccine target
Yes, he said in his opening remarks that vaccinating 15 million people by the government's target date of 15 February was "an unprecedented national achievement".
But then, straightaway, the prime minister said it was "no moment to relax".
It was a huge step forward in the fight against COVID, but only a first step, he warned the public.
"We want this lockdown to be the last," said Mr Johnson. "And we want progress to be cautious but also irreversible."
Cautious and irreversible. In other words, no more embarrassing lockdown U-turns. No more promising what he can't - or may not be able to - deliver.
But the prime minister's caution, when the vaccination programme has been so successful so far, will infuriate those Conservative MPs demanding a speedy end to the lockdown in England.
'We want this lockdown to be the last'
![UP NEXT]()
UP NEXT
In some ways, the huge success of the vaccine programme has made Mr Johnson's decisions on easing lockdown measures harder, not easier.
If the over-50s are vaccinated by the end of April, as the prime minister said at his news conference he hoped they would be, there's no need for any of the restrictions any more, his backbenchers claim.
If only it were that simple, the prime minister must be thinking.
And the boffins - led by England's chief medical officer Professor Chris Whitty, who was alongside Mr Johnson at this news conference - are arguing the very opposite of the MPs' case.
In answer to Sky News' deputy political editor Sam Coates, Prof Whitty spoke about "some residual risk" after mass vaccinations.
Sir Simon Stevens, the NHS England chief executive, said: "It's definitely not mission accomplished."
In fact, on this occasion the answers by Prof Whitty and Sir Simon were more candid and informative than those of the prime minister, who was clearly determined to give nothing away until next Monday - when he unveils his roadmap for easing lockdown.
With parliament not sitting this week, Mr Johnson will hope he can control the political agenda better, staging news conferences when he wants and without his pesky backbenchers carping on in the House of Commons.
Fat chance of that, though. While he urged the public to take speculation about the government's plans "with a pinch of salt", the news vacuum may give more air time and column inches to his opponents.
So far, so good, though. The Tory high command and the prime minister's inner circle in Downing Street will be delighted by evidence this weekend of a "vaccine bounce" for Mr Johnson and the Conservative Party in opinion polls.
But complacency now - and problems in the next few weeks like interruptions or shortages in vaccine supplies - could suddenly change that.
His Tory critics will be even more unforgiving then.
Subscribe to the Daily podcast on?Apple Podcasts,?Google Podcasts,?Spotify,?Spreaker
There's also the possibility that the government's controversial quarantine hotels policy, launched this week, could go horribly wrong or that another new COVID variant could pose a dangerous threat to the nation's recovery.
So prudence and caution, words not normally associated with this prime minister, will be the strategy for the next seven days.
That's why, all of a sudden, Mr Johnson has become disciplined and relentlessly on message.
No more silly talk of "moon shots" and "world-beating" initiatives. And definitely no gloating.