More than half of the UK's adult population has now had two doses of a coronavirus vaccine.
Vaccines minister Nadhim Zahawi confirmed the achievement, tweeting: "Another Important milestone today. 50% of all adults in the U.K. have had the protection of two doses.
"Thank you to a brilliant team. We keep going."
On Wednesday, it was announced that three-quarters of adults in the UK had received a first jab.
A total of 26,422,303 second doses have now been delivered - equivalent to 50.2% of the adult population - since the vaccination rollout began last December.
In England, 22,442,383 second doses have been given - equivalent to 50.7% of the adult population.
England is slightly ahead of the other three nations of the UK, with Scotland on 48.2% (2,137,618 second doses), Northern Ireland on 47.1% (684,398 second doses), and Wales on 45.9% (1,157,904 second doses).
Health Secretary Matt Hancock said he was "thrilled" with the figures - as he urged people to take up the offer of a jab.
"Let's roll up our sleeves and put this pandemic behind us, once and for all," he added.
But Britain has reached a "dangerous moment" in the pandemic, according to an expert - amid warnings that "vaccine beating variants" will emerge in the future.
And it comes as coronavirus case rates have increased or stayed level across all age groups over the last week, Public Health England (PHE) figures showed.
The most significant spike in cases is among people aged between 10 and 29, many of whom are yet to have a jab, according to PHE data.
There were 72.3 cases per 100,000 people among this age group in the week up to 30 May - rising week-on-week from 55.1.
The second highest rate is among those aged 20-29 - increasing from 31.6 to 52.0 per 100,000.
Dr Mike Gent, incident director for the COVID-19 response at PHE, said: "We are getting some increases in case rates once again, particularly in younger age groups who are not yet being vaccinated and are having regular testing."
He said this was "to be expected" as the country opens up and people begin to socialise.
The government intends to offer all adults in the UK a first dose by the end of July.
It has set a target of offering both doses to everyone aged 50 and above by 21 June - the same day Prime Minister Boris Johnson hopes to lift all coronavirus restrictions in England.
But ministers have been urged to delay stage four of the roadmap, when all legal limits on social contact will be removed, for at least a month due to the spread of the India variant - now renamed as the Delta variant.