For a month, the European Union’s top executive, Ursula von der Leyen, had been exchanging texts and calls with Albert Bourla, the chief executive of Pfizer. Two things became clear: Pfizer might have many more vaccine doses it could offer the bloc. And the European Union wanted them.

That personal diplomacy played a big role in a deal, to be finalized this week, in which the bloc will lock in 1.8 billion doses from Pfizer.

The deal will establish the European Union as Pfizer’s biggest client and allow the bloc to resell or donate the vaccines to partners, empowering it to support poorer countries’ struggling immunization efforts.