UK experts are set to recommend all 16 and 17-year-olds should be offered a Covid vaccine, the BBC has been told.
The Joint Committee on Vaccination and Immunisation stopped short of making the move last month, saying it was still assessing the benefits and risks.
About 1.4 million teenagers will be included in the new rollout but it is not known when the jabs will start.
They are only offered now to those over-12s who have underlying conditions or live with others at high risk.
But some countries, including the US, Canada and France, are routinely vaccinating people aged 12 years old and over.
Whitehall sources say ministers in England are expected to accept the advice of the JCVI, following an announcement on Wednesday.
It comes after Scotland's First Minister Nicola Sturgeon said on Tuesday she was "hoping" to receive updated advice from the JCVI on the vaccination of 16 and 17-year-olds.
Ms Sturgeon said the UK's four chief medical officers had written to the JCVI, asking them to look again at vaccination advice for young people.
Universities Minister Michelle Donelan said an announcement was "imminent and... people will get clarity soon".
Meanwhile, new research suggested children who became ill with coronavirus mostly recovered within less than a week.
Across England, 223,755 under-18s have received a first vaccine dose, according to NHS data to 25 July.
It was previously announced that under-18s would be eligible if they had certain health conditions, lived with someone with a low immune system, or were approaching their 18th birthday.
But there was criticism after it emerged GPs were advised to hold off inviting clinically vulnerable 12 to 15-year-olds to take a vaccine due to uncertainty over insurance.
What are your questions about the vaccine for teenagers?
Decisions on vaccinations are based on recommendations from the independent JCVI. Ministers in England, Wales, Scotland and Northern Ireland each then approve the plans.
The only Covid jab currently authorised in the UK for under-18s is the Pfizer-BioNTech vaccine.
Last month, the JCVI extended its recommendation on Covid jabs to children aged over 12 who are at higher risk of being ill and to those on the verge of turning 18.
However, it said it would not extend the rollout as it examined reports of rare adverse events such as inflammation of heart muscles among young adults.
Speaking ahead of the July decision, England's chief medical officer Prof Chris Whitty said the JCVI was confident vaccines would protect children to a high degree.
He added more research was taking place as children did not tend to suffer severely from Covid, and the experts wanted to ensure the benefits of the jab outweighed any potential risks.
Evidence to press ahead
The decision to vaccinate children has always been more delicately balanced than for adults.
Children have less to gain from a Covid jab, not because it is less effective, but because they rarely become severely ill.
And while the risks of side effects such as inflamed heart tissue (which is often treated with rest and ibuprofen) are incredibly rare, they do exist.
Very high levels of vaccination in the most vulnerable also weakened arguments of immunising the young so they can't spread it to the old.
On top of that, the JCVI did not want to accidentally damage confidence in the usual childhood vaccines (from measles to meningitis to HPV) if a decision was seen as rushed or putting children at unnecessary risk.
It has been a decision that has been made slowly (too slowly for some) but now, after other countries have vaccinated hundreds of thousands of children, the evidence is there to press ahead.
Prof Paul Elliott, chair of epidemiology and public health at Imperial College London, told BBC Radio 4's Today programme vaccinating younger age groups could help drive down infections.
With the highest rates of infection seen in young people under 24, he said "anything we can do to reduce transmission in that group would be helpful".
But school leaders' union NAHT said the policy of vaccinating children should be led by clinicians and that schools should not play a part in promoting or enforcing vaccinations.
One local director of public health, Dr Anjan Ghosh, told BBC Radio 4's World at One it was likely parents and guardians would be asked for consent before some under-18s received a vaccine dose.
"Whether it is done in a school, or any other setting, the consent is about allowing the child to be vaccinated - so it doesn't depend on the setting where vaccines are happening from," he said.
Previous guidance said the over-16s would give their own consent for jabs, while for those under-16 parents or guardians would be involved in giving consent as well.
Shadow health secretary Jonathan Ashworth said ministers should "ensure plans are in place to roll out this vital next stage of vaccination while ensuring parents have all the facts and information they need".
A Department of Health and Social Care spokesperson said it kept the vaccination of children and young people "under review and will be guided by the advice of the independent Joint Committee on Vaccination and Immunisation".
All over-18s have now been offered a vaccination against coronavirus. The latest government data shows 88.7% of adults in the UK have now had one dose of vaccine, while 73% have had two jabs.
And a further 21,691 cases of people testing positive for coronavirus were recorded in the UK on Tuesday. It was the fifth day in a row that infections have fallen, and the lowest daily total since late June.