Medical workers in Oaxaca, Mexico, line up before working on a late-stage vaccine trial from Chinese pharmaceutical company CanSino Biologics on Nov. 6. (Jorge Luis Plata/Reuters)

BERLIN — In the new frontier of vaccine diplomacy, there are two paths: stockpile or share.

The first way is unfolding in the United States — with two promising coronavirus vaccines by Pfizer and Moderna on the cusp of approval — as the Trump administration focuses on domestic distribution from private labs.