"The EU reached a deal with Pfizer in November for 300 million doses and in January negotiated a preliminary deal for another 300 million." https://www.dw.com/en/eu-orders-300-million-more-biontech-pf...
USA agreed to buy 100-500 Million in JULY 2020 https://edition.cnn.com/2020/07/22/health/pfizer-covid-19-va...
The fact is that EU is too slow, too risk adverse and 28 countries must agree. In USA the President winks, and it's done. (In this case it was beneficial.)