US President Joe Biden has called for states to offer $100 (£71) to the newly vaccinated in an effort to address flagging jab rates amid virus surges.
The president also issued a strict new vaccine requirement for US federal workers, the nation’s largest workforce with some two million people.
The order requires employees to show proof of vaccination or be subjected to mandatory testing and masking.
Just under half of the US is fully vaccinated, according to official data.
Speaking from the White House on Thursday, Mr Biden said that the new measures are a result of the highly contagious Delta variant’s spread, made worse by a “pandemic of the unvaccinated”.