Until now, the fastest vaccine ever made - for mumps - took four years. And while our current effort to develop a covid-19 vaccine involves thousands of people working around the clock, the mumps vaccine was developed almost exclusively by one person: Maurice Hilleman. Hilleman cranked out more than 40 other vaccines over the course of his career, including 8 of the 14 routinely given to children. He arguably saved more lives than any other single person. And through his work, Hilleman embodied the instincts, drive, and guts it takes to marshall the human body’s defenses against a disease. But through him we also see the struggle and the costs of these monumental scientific efforts.