Pfizer-BioNTech vaccine, officials have said that advice about second doses will be given at a later date, while more data is gathered.
Britain's Joint Committee on Vaccination and Immunisation (JCVI) initially declined to recommend shots for all 12- to 15-year-olds, citing uncertainty over the long-term impact of myocarditis, a rare side effect of mRNA-based vaccines such as Pfizer's.
The heart condition typically resolves itself with mild short-term consequences, health experts have said. Hong Kong has advised children only get one shot, owing to similar concerns over heart inflammation.
The study, called Com-COV3, will test different vaccine schedules in 12- to 16-year-olds, looking at the immune responses and milder side-effects. "T