Around 500 children will be eligible, including those receiving chemotherapy or radiotherapy, those with leukaemia, diabetes, chronic diseases or severe mental illness, and those who live with someone who is immunosuppressed.
They are entitled to their booster three months after their two primary vaccine doses, while severely immunosuppressed children can get their booster after a third primary dose.
Those who have tested positive for Covid-19 must wait 12 weeks before getting their booster, or at least four weeks if they are in the highest risk groups.
Watch: NHS staff in England give booster jab to four in five eligible adults
GPs have already begun sending out invites to the parents or guardians of eligible children, encouraging them to secure an appointment through a local booking system.
The youngsters can also get the jab at hospital hubs, via their GP, through a home visit or by going to a walk-in vaccination site – as long as they show their NHS invitation letter.
Parents are asked to accompany their children.
The NHS vaccination programme lead for 12-15s, Nick Hulme, said: “The booster has been proven to give substantial levels of protection against Covid-19 and the new Omicron variant, so it is vital that our youngest and most at-risk get their top-up dose of protection as soon as possible.
“I am delighted that we can kick off this stage of the rollout with the most at-risk children eligible from today, and we look forward to encouraging many more to come forward in the coming days and weeks.
“As soon as you receive the invitation from your local NHS team or GP, please do take up the offer and bring your child forward for their all-important protection as soon as you can.”
Four in five eligible adults have now had their COVID-19 booster vaccine in England!
If you’re due your COVID-19 booster jab, please come forward as soon as you can to best protect yourself and those around you. Book online and #GetBoostedNow. https://t.co/ocH1SqGFXG pic.twitter.com/L1vyZjoynM
— NHS England and NHS Improvement (@NHSEngland) January 16, 2022
Recent data from the UK Health Security Agency (UKHSA) showed that two doses of the vaccine are not enough to stop people becoming unwell from Omicron, but a booster significantly increases protection against the variant.
From Monday, 16 and 17-year-olds will also be eligible for their top-up dose.
Since the vaccination campaign opened to all 12 to 15-year-olds in September, more than 1.4 million in that age group have had their first dose. The cohort is also eligible for a second dose 12 weeks after their first.
In total, more than 114 million doses have been delivered in England since December 2020, including more than 30 million top-up doses.
Watch: Why are millions of people not yet vaccinated against coronavirus?