The Moderna Spikevax COVID-19 vaccine has been approved for 12 to 17-year-olds by the Medicines and Healthcare products Regulatory Agency (MHRA). It is already approved for 18s and over.
The Joint Committee on Vaccination and Immunisation (JCVI) is yet to issue advice on deploying the vaccine to this group.
MHRA Chief Executive, Dr June Raine, said: "I am pleased to confirm that that the COVID-19 vaccine made by Moderna has now been authorised in 12 to 17-year-olds. The vaccine is safe and effective in this age group.
"We have in place a comprehensive safety surveillance strategy for monitoring the safety of all UK-approved COVID-19 vaccines and this surveillance will include the 12 to 17-year age group."
An MHRA statement said: "No new side effects were identified and the safety data in children was comparable with that seen in young adults. As in young adults, the majority of adverse events were mild to moderate and relating to reactogenicity, such as a sore arm or tiredness."
The MHRA approval covers Great Britain and came through the European Commission (EC) Decision Reliance Route, under which the manufacturer's application references the European Medicines Agency's (EMA) decision. Northern Ireland was already covered under an EMA extension in July.
The Pfizer/BioNTech vaccine is already approved for use in the UK for people aged 12 and over.