An estimated 5.3 million booster doses of Covid-19 vaccine have been delivered in the UK, new figures show.
It is the first time data on boosters has been reported by all four nations.
It means around one in nine people in the UK who have received a first and second dose of vaccine are likely to have also received a booster.
The figures have been published by NHS England Public Health Scotland, Public Health Wales and the Northern Ireland Department of Health.
The total for England includes a small number of third primary doses of vaccine, NHS England said.
Wales currently leads the other nations in the proportion of double-jabbed people who have also received a booster, at 14.4%, according to analysis by the PA news agency.
The equivalent proportion for England is 11.9%, with 11.1% for Scotland and 3.5% for Northern Ireland.
A breakdown by age group suggests more than half of double-jabbed people aged 80 and over in England have now had a booster (53.6%), compared with just under a half (47.2%) in Wales.
Some 39.8% of eligible 75 to 79-year-olds in England have also had a booster, along with 30.6% in Wales.
Data on booster take-up among age groups in Scotland and Northern Ireland is not yet available.
Prime Minister Boris Johnson described the milestone as “fantastic”, adding: “It’s vital that you take up your booster jab when you’re offered it this winter.”
While Health Secretary Sajid Javid said: “Hitting over five million booster jabs across the UK is a fantastic achievement as we keep ahead in the race between the vaccine and the virus.
“Getting your booster jab is one of the most important things you can do this winter to keep building our wall of defence against the virus and stop you becoming seriously ill from Covid-19.
“I urge all those eligible to book their booster and flu vaccines soon as possible to maintain your protection.”
Dr Nikki Kanani, deputy lead for the NHS vaccination programme, said: “The NHS Covid vaccination programme continues to accelerate at speed and it is fantastic that in just one month, more than five million booster doses have been delivered across the UK, including over 4.5 million in England alone.
“Hundreds of thousands of people continue to book in for their vital boosters every day, including almost half a million on Wednesday and Thursday this week, and with millions more set to receive invites next week, I would urge everyone to book in as soon as possible to get crucial protection this winter.
“The booster is not simply a nice to have, it will provide important extra protection as we go into the winter period.
“So if you have been invited or a family or friend has been invited, please do come forward.”