Coronavirus vaccines are now being offered to people aged 42 and over in England.
It is the second time this week the vaccine booking system has been extended to more people in their 40s, after they were offered to those aged 44 and over yesterday.
Now, people aged 42 and over, or those who will turn 42 before 1 July, can arrange their jab appointment through the national booking website.
Health Secretary Matt Hancock, 42, urged those eligible to come forward and said he was "standing by" his mobile phone waiting for a text message as the next age group "includes me".
In a video post on Twitter, he said: "I’m really looking forward to getting my text. Yesterday we opened up to people aged 44 – that’s gone very, very well, thank you to the hundreds of thousands who’ve come forward and booked your appointment, and now we’re able to go that little bit further.
"This vaccination rollout is going incredibly well. The uptake is astonishingly high."
The expansion of the vaccine programme comes as figures over the weekend confirmed more than half of the UK’s total population has received a first dose of a COVID-19 vaccine.
Government data up to 25 April shows that of the 46,650,008 jabs that have been given in the UK so far – 12,897,123 were second doses.
The target of offering a first coronavirus vaccine dose to the nine most vulnerable groups by 15 April was reached three days early.
Despite supply constraints and second jabs for those at highest risk of contracting COVID being prioritised, the rollout was subsequently slowly expanded to adults under the age of 50, with people in their mid to late 40s the first group to be offered the jab as part of this second phase.
Within a week of the booking system opening, two thirds of 45 to 49-year-olds had received their first vaccine.
A new campaign called "every vaccination gives us hope" has been launched this week and includes a TV advert showcasing the health workers and volunteers involved in the UK’s vaccination rollout.
During a visit to Wrexham on Monday, Prime Minister Boris Johnson urged people to take up the vaccine when offered it.
He also urged the public to be "realistic" about the prospect of the UK being hit with a third wave of COVID-19.
"We have built up what I think are some pretty robust fortifications against the next wave, we will have to see how strongly they really are in due course," he said.
The PM denied saying he was prepared to let "bodies pile high" rather than order another lockdown, rebuffing newspaper allegations that he had made the comments in October, just prior to England’s second national lockdown.
Asked if he had ever made those remarks, Mr Johnson said: "No. The important thing I think people want us to get on and do as a government is to make sure that the lockdowns work and they have.
"I really pay tribute to the people of this country, this whole country of ours, that have really pulled together and – working with the vaccination programme – we’ve got the disease under control."
Vaccinations are now being administered at more than 1,700 sites across England, including at GP surgeries, pharmacies, places of worship, football grounds and supermarkets.
Meanwhile, in Scotland, preparations continue to extend the vaccine rollout to people in their 40s, while those aged 30 and over are being offered the jab across Wales.
In Northern Ireland, as well as the clinically vulnerable, people aged 35 and over have been invited to book their vaccine appointment.