That is one of my points, EU should have played it differently. How many doses did they export to the USA?The EU has exported about 35 million vaccine doses so far, including to the UK and the US (around 10 million to the UK in total so far). Return flow, I believe, has been zero. EU officials should've studied game theory more.
EDIT: I will concede that since the USA has enough P, M, J&J on order to vax the country, they could keep the 10 mil AZ doses, but share some of the 30 mil as they come online (Koronin might be right, USAers might not want AZ). But as we can see by this exchange, sharing can leave you short.