The US government has ruled out introducing mandatory Covid-19 vaccination passports. The White House has said that citizens' privacy and rights should be protected.
Schemes to introduce such passports have been proposed around the world as a way to enable safe ravel of people while fighting the coronavirus pandemic.
But critics of the vaccine passport proposal say such documents could be discriminatory.
The US has said it did not and would not support a "system that requires Americans to carry a credential".