Scientists are looking at whether children need a second dose of coronavirus vaccine and if so which type would be best.
It comes after health leaders approved first doses of the Pfizer vaccine for over-12s on Monday.
Researchers are launching a study of Covid-19 vaccination schedules in young people aged 12 to 16.
The Com-Cov 3 trial will seek to recruit 360 volunteers who will be enrolled in one of four arms of the study.
Professor Matthew Snape, associate professor in paediatrics and vaccinology at the University of Oxford, and chief investigator on the trial, said: “This study will provide vital information on the range of options for immunising teenagers against Covid-19 in the UK.
“As well as looking at the standard two full doses of the Pfizer vaccine, we will look at how well volunteers respond when their second dose of Pfizer is half that of the first dose, or if different vaccines are used altogether, such as the vaccines manufactured by Moderna or Novavax.
“This will provide the JCVI (Joint Committee on Vaccination and Immunisation) with information crucial to informing their advice about immunising teenagers in the UK.”
Participants will either receive two Covid-19 vaccine doses in the study, in which case their first dose will be the Pfizer jab.
Alternatively, those who have already received a dose of the Pfizer Covid-19 vaccine through the NHS can be enrolled at the time of their second dose.
Participants will be randomly allocated at the time of the second dose to receive either a full dose or half dose of the Pfizer-BioNTech vaccine, a full dose of the Novavax jab or a half dose of the Moderna vaccine.
The study is backed through funding from the Vaccines Taskforce and National Institute for Health Research (NIHR) and run across four NIHR-supported sites by the National Immunisation Schedule Evaluation Consortium.
Professor Andrew Ustianowski, NIHR clinical lead for the Covid-19 vaccination programme and joint national infection specialty lead, said: “It is important to establish the most effective vaccine doses for different population groups, and this latest study will help develop our understanding of immune responses for young people once vaccinated against Covid-19.”
Researchers hope to report initial results by December, and if the results are promising, regulators the Medicines and Healthcare products Regulatory Agency (MHRA) and JCVI would formally assess the safety and efficacy of any new vaccination process before advising whether it is rolled out to patients.
Anyone who is interested can register on comcovstudy.org.uk.