However, the US government was able to block export of AstraZeneca, apparently due to having purchased the vaccine:
The U.S. Is Sitting on Tens of Millions of Vaccine Doses the World Needs https://www.nytimes.com/2021/03/11/us/politics/coronavirus-a...
US agrees to share AstraZeneca vaccines with Mexico, Canada https://amp.france24.com/en/americas/20210319-closing-in-on-...