Video report by ITV News correspondent Juliet Bremner
Some 300 volunteers are taking part in the trial to assess whether the jab can produce a strong immune response in children aged between six to 17.
The first vaccinations under the trial began on Tuesday and are taking place at four different centres in the UK. 240 children will get the vaccine, while the others will receive a control meningitis jab.
Meara, aged 16, saw the opportunity to volunteer on Twitter. She says she is taking part in the trial in an attempt to "make a difference".
"It is quite strange but I'm feeling really lucky to have been given the opportunity to have the vaccine," the schoolgirl said.
Her mum, Sarah, echoed this sentiment: "She was looking for something throughout the whole of the pandemic to play a part in improving the future for everybody.
"I'm really proud that she's wanted to take part."
16-year-old Tilda volunteered after her mother heard about the trial on the radio.
Tilda said: "We live relatively nearby, so when I heard it was going on here, I thought, 'if I can do my bit to help, then why not?'"
"I think it's really exciting."
The Oxford jab is one of three to have been approved for use in adults in the UK, along with those from Pfizer/BioNTech and Moderna.
The University of Oxford said theirs was the first trial in the six-17 age group. It said other trials had begun but only measuring efficacy in those aged 16 and 17.
Twelve-year-old volunteer Sylvia got involved as her dad was on the adult trial and she "just want to do something".
She said: "It would just try and help get rid of this virus quicker and just get things back to normal quicker."
Sylvia will return in four weeks for a second jab.
Her dad, James, said: "I’m really proud of her. Even having a jab can be quite intimidating and the setup here is quite clinical and bright and it could be a bit intimidating.
"But she's been really brave, and she's really gone for it."
The Royal College of Paediatrics and Child Health has said there is evidence Covid-19 can cause death and severe illness in children, but that this is rare.
So, why are researchers running a trial on youngsters if they're not especially vulnerable to coronavirus?
Hannah Robinson, Lead Clinical Delivery Nurse for the Oxford Vaccine Group, explained: "We want to know that there is a similar immune response so that the children are protected and we want to know more information about the effect of the vaccine."
Scientists also hope that if the trials are successful, vaccinating children could help to reduce the spread of the virus.
Earlier this month England's Deputy Chief Medical Officer Professor Jonathan Van-Tam told ITV News it is "perfectly possible" that the UK will have some licensed children's vaccines for Covid-19 by the end of the year.
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