President Joe Biden wants 70 per cent of American adults to have received at least one shot of a Covid-19 vaccine by the July 4 holiday, and has made vaccinating adolescents a key part of the next phase of the country's immunization 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, according to AFP.

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.

An emergency use authorisation is expected in the coming days, and Biden told White House reporters that “if that announcement comes, we are ready to move immediately”.

The president's address comes as the nation's immunisation campaign is stalling after hitting a peak in early April.