While Gates’ vaccine-based giving—closing in on $6 billion to fight measles, hepatitis B, rotavirus and AIDS, among others—is part of the largest, most human-driven philanthropy in the history of mankind, what’s missing in his language are the individual ­humans.

In many ways that’s the point. Gates’ clipped manner in discussing the children he and his wife met in India and Africa (“Melinda and I spend time with these kids, and we see that they’re suffering; they’re dying”) disappears when the underlying numbers come up, his speech getting more rapid, his voice ever higher. “A 23-cent vaccine,” he says, “and you’ll never get measles,” a disease that “at its peak was killing about a million and a half a year; it’s down below 300,000.” Gates rattles off milestones in the history of global health and the prices of vaccines down to the penny, but blanks on the name of one of his favorite vaccine heroes, John Enders, the late Nobel laureate, or Joe Cohen, a key inventor of the new malaria vaccine Gates helped bankroll.