Sixteen and 17-year-olds across the UK are now being invited to book their Covid vaccine.
GPs in England have been told they can contact this age group, while invites are also being sent out in Wales.
In Northern Ireland, walk-in centers are now open to older teenagers, and in Scotland, they can register their interest online.
Meanwhile, new figures show most patients in hospitals with Covid in England continue to be unvaccinated.
The opening of vaccinations to 16 and 17-year-olds in England comes amid a drive to encourage young people to get jabbed.
The vaccine’s benefits will be promoted to partygoers in nightclubs, including the Ministry of Sound and Heaven.
A campaign will also be rolled out across social media channels including Facebook, Instagram, Twitter, Snapchat, and TikTok, as well as on radio stations Kiss, Capital, Heart, Sunrise, and TalkSport, urging young adults to get jabbed.
Walk-in centers in England will accept people aged 16 and 17 from next week, but those in that age group are currently unable to book an appointment using the NHS website.
In Northern Ireland people aged 16 and up have begun to get the vaccine.
Elliot Aston, 16, from Newtownards, told the PA News Agency it was good his age group was able to get the jab as “we are probably the ones that are out and about the most”.
Bethany Holden, 16, who was among the first to receive the vaccine at the SSE Arena in Belfast on Friday, said she was glad to get the job as she was “more protected and protecting other people as well”.
Children aged 12 to 15 who are clinically vulnerable to Covid or live with adults who are at increased risk of serious illness from the virus will be contacted by the NHS and invited for their vaccine over the coming weeks, NHS England said.
Jabs will also be offered to children aged 12 years and over who live with someone who is immunosuppressed, such as those receiving chemotherapy or who have had a transplant, with NHS England saying more than a million children and young people could now get the jab.
Health Secretary Sajid Javid said the vaccines were “building a wall of defence against the virus” and were “the best way to protect people from serious illness”.
Since 19 July, 1,467 people have been admitted to hospital with cases of the Delta variant, Public Health England (PHE) said.
Out of these 808 (55.1%) were unvaccinated, while 512 (34.9%) had received both doses.
PHE said: “While vaccines provide high levels of protection, they are not 100% effective and will not stop everyone catching Covid-19.
“As more of the population gets vaccinated, we will see a higher relative percentage of vaccinated people in hospital.”
Dr Jenny Harries, chief executive of the UK Health Security Agency, stressed vaccines would not eliminate all risks and it was still possible to become unwell with Covid-19 and infect others.
“It is still vital that we exercise caution, particularly while cases are high,” she added.
Some 88.8% of the UK’s adult population have now had one dose of a coronavirus vaccine, while 73.8% have had both jabs.
Delta remains the dominant variant in the UK, making up about 99% of cases.