Health Secretary Sajid Javid has said the NHS in England will now begin rolling out the vaccine to children aged between 12-15.
The move comes after the chief medical officers of the four UK nations advised younger teenagers should be offered the Pfizer/BioNTech jab.
They said their decision takes into account the “extremely powerful” evidence on the impact of the pandemic on children’s education, as well as the risks to their mental health from missing school.
Mr Javid said the NHS in England would now begin rolling out the vaccine with the same urgency that has characterised the rest of the programme.
“I have accepted the recommendation from the chief medical officers to expand vaccination to those aged 12 to 15 – protecting young people from catching Covid-19, reducing transmission in schools and keeping pupils in the classroom,” he said.
“Our outstanding NHS stands ready to move forward with rolling out the vaccine to this group with the same sense of urgency we’ve had at every point in our vaccination programme.”
Health chiefs on Monday gave the go-ahead for Covid-19 jabs for children but warned it would not be “a silver bullet” stopping schools closing.
England’s Chief Medical Officer Professor Chris Whitty and his counterparts from Scotland, Wales and Northern Ireland approved the roll-out of the Pfizer/BioNTech vaccine to healthy 12 to 15-year-olds.
They have recommended at this time they get one dose with advice on a second dose not being given until the Spring.
Speaking at a press conference in Downing Street, Professor Whitty said they had considered the medical benefits of the vaccine and the impact of Covid-19 on disruption to education.
He said the evidence they heard was that “the disruption in education which has happened over the last period since March 2020 has been extraordinarily difficult for children and had a big impact on health, mental health and public health”.
“This is most apparent in areas of deprivation,” he said, adding that vaccination “will reduce education disruption” but “we do not think this is a panacea, it is not a silver bullet”.
“We think it is an important and potentially useful additional tool to help reduce the public health impacts that come through educational disruption,” he said.
He also told reporters that vaccinating children would not have any effect on supplies for booster jabs and that there are “no plans” to vaccinate children under 12.
He told a Downing Street press conference on Monday: “We certainly have no plans at the moment to re-examine this, there are some nations that are doing this.
“It hasn’t even got to the point where this has been considered by MHRA, so we’re a long way even thinking about this, so let’s not rush that one at all.”
The move means around three million children could be eligible for the jab and comes despite the Joint Committee on Vaccination and Immunisation (JCVI) deciding not to recommend mass vaccination of 12 to 15-year-olds.
The JCVI had said Covid-19 presents a very low risk for healthy children and vaccination would only offer a marginal benefit, but the Chief Medical Officers (CMOs) said other factors, such as school disruption, tipped the balance given the virus was going to keep spreading over Winter.
It is expected the vaccinations will be given through schools.
The vaccines have already been cleared as safe for use in children by the Medicines and Healthcare products Regulatory Agency.
In their advice to the Government, the UK's CMOs said they were recommending vaccines on "public health grounds" and it was "likely vaccination will help reduce transmission of Covid-19 in schools".
They added: "Covid-19 is a disease which can be very effectively transmitted by mass spreading events, especially with Delta variant.
"Having a significant proportion of pupils vaccinated is likely to reduce the probability of such events which are likely to cause local outbreaks in, or associated with, schools.
"They will also reduce the chance an individual child gets Covid-19. This means vaccination is likely to reduce (but not eliminate) education disruption."
The CMOs have asked for the JCVI now to look at whether second doses should be given to children and young people aged 12 to 15 once more data comes through internationally. This will not be before the spring term.
The CMOs think a single dose will reduce significantly the chance of a young person getting Covid and passing the virus on.
After seeking advice from a range of experts, the CMOs said they consider education "one of the most important drivers of improved public health and mental health".
They added: "The effects of disrupted education, or uncertainty, on mental health are well recognised.
"There can be lifelong effects on health if extended disruption to education leads to reduced life chances.
"Whilst full closures of schools due to lockdowns is much less likely to be necessary in the next stages of the Covid-19 epidemic, UK CMOs expect the epidemic to continue to be prolonged and unpredictable.
"Local surges of infection, including in schools, should be anticipated for some time. Where they occur, they are likely to be disruptive."
It came as Professor Neil Ferguson, the Imperial College London scientist whose work was key to the first lockdown in March 2020, also backed booster doses to reduce the spread of the virus, as well as protecting individuals. The top epidemiologist told how the UK had fallen behind in the race to get its citizens vaccinated.
“We were leading in Europe until recently,” he told BBC Radio 4’s Today programme earlier.
“Now several countries, Spain, Portugal, France, Italy, Ireland, have got higher vaccination levels than us. That’s largely because they have rolled out vaccination of 12 to 15 year olds faster than us.”
With cases having risen in the UK in recent weeks, he said: “If we want to stop the risk of the large autumn and winter wave we need to boost immunity in the population.”
Pressed if this should be done by vaccinating more teenagers, he added: “That is the initial priority because it is going to take six to eight weeks from starting before those teenagers have had two doses.”
Doctors and teachers in London said they were ready to rapidly vaccinate these age groups as soon as the green light was given.
Preparations in some boroughs are at an advanced state, the Standard has learned.
The nature of the roll-out may vary by borough but is likely to centre on pop-up clinics in secondary schools.
Teams of vaccinators previously trained to give the jab to adults are on standby.
GPs say the only concerns will be the need for schools to ensure parental consent has been received, and space to enable pupils who receive the vaccine to be observed for 15 minutes afterwards.
Professor Ferguson explained that as Britain got off to such a quick start, this was now being affected by the vaccine’s effectiveness “decaying” over time.
The Pfizer jab is also more effective against the Delta variant, which has spread so fast, than the Oxford/AstraZeneca vaccine and the former has been more widely used on the Continent than in the UK, he added.
The JCVI was to meet today to discuss the scale of the booster roll-out, which is expected to start with the over-70s.