US President Joe Biden wants 70% of American adults to have received at least one shot of a Covid-19 vaccine by the 4 July holiday and has made vaccinating adolescents a key part of the next phase of the country's immunisation campaign.
But targeting US teens is a controversial move among many experts, who argue it is a serious mistake to use the world's limited supply of doses on a low-risk population while the pandemic surges in countries like India and Brazil.
Pfizer and its partner BioNTech said in March their two-dose regimen was shown to be safe and highly effective in a trial of 2,260 12-to-15-year-olds.