From the G7 agenda reporting: “ Last Friday morning, during an interview on Good Morning America, U.S. Homeland Security Secretary Alejandro Mayorkas said the Biden administration was taking “a very close look” at the possibility of vaccine passports for travel into and out of the United States. However by Friday afternoon the Department of Homeland Security was clarifying Mayorkas’ statement. The DHS says there won’…
The UK has also ruled it out. I wouldn't use one - emigrate or never travel. https://www.telegraph.co.uk/politics/2021/05/30/uk-vaccine-p...
As far as I can tell they're still very much planned for inbound international travel to the UK, and they're already in use for outbound international travel - the NHS app is accepted as proof of vaccination status at the border when entering quite a few countries e.g. Greece https://www.gov.uk/foreign-travel-advice/greece/entry-requir...