On Monday, the FDA also shortened the time for booster shots from at least six months after completion of the initial series to at least five months, for everyone aged 12 and older, reports Xinhua news agency. 

The agency has determined that the protective health benefits of a single booster dose of the Pfizer-BioNTech Covid-19 vaccine to provide continued protection against the virus and the associated serious consequences outweigh the potential risks in individuals aged 12 to 15. 

The agency said that it found "no new safety concerns" following a booster shot in young teenagers, and that there were no new reports of two types of heart inflammation called myocarditis or pericarditis linked to the boosters. 

The decision came as the Omicron variant is spreading rapidly across the US and has led to record high hospitalisations among younger people.