The US will begin sharing its entire pipeline of vaccines from AstraZeneca once the jab clears federal safety reviews, the White House has said.
As many as 60 million doses are expected to be available for export in the coming months.
The move greatly expands on Joe Biden administration's action last month to share about four million doses of the vaccine with Mexico and Canada.
The AstraZeneca vaccine is widely in use around the world but not yet authorised by the US Food and Drug Administration.
The White House is increasingly assured about the supply of the three vaccines being administered in the US, particularly following the restart of the single-dose Johnson & Johnson jab.
"Given the strong portfolio of vaccines that the US already has and that have been authorised by the FDA, and given that the AstraZeneca vaccine is not authorised for use in the US, we do not need to use the AstraZeneca vaccine here during the next several months," said White House Covid-19 co-ordinator Jeff Zients.
"Therefore the US is looking at options to share the AstraZeneca doses with other countries as they become available."
