PEPFAR didn’t end AIDS, but in more than 50 countries around the world, it brought the crisis under control. Since Mr. Bush launched PEPFAR in 2003, it has invested more than $85 billion in AIDS treatment, prevention and research; it has saved, at a conservative estimate, 20 million lives. It was the Marshall Plan of modern health care, the largest ever commitment to combat a single disease globally.

Many countries are looking to Mr. Biden for the sequel. Like AIDS treatment for whoever needed it, the case for a global Covid-19 vaccine program is a moral one. But there’s also a self-interested argument for America to play the leading role, too: An international vaccine program is an investment in the U.S. economy, an act of national security and a good bet on individual good health.

Everyone knows what needs to be done. Everyone is waiting for someone else to do it. To turn this diplomatic game of hot potato into an effective program, and if the U.S. is going to lead the global vaccine rollout, rather than allow China to take that role, the Biden administration would need a high-profile emissary.