Jonas Salk’s polio vaccine transformed America and the world in ways that seemed unimaginable. But in 1955, there was a moment when everything was in doubt. This week, Josh Levin talks with Dr. Paul Offit about the medical mystery that threatened to derail one of history’s most important scientific breakthroughs.

Josh Levin is One Year’s editorial director. One Year’s senior producer is Evan Chung.

This episode was produced by Kelly Jones, Evan Chung, and Sophie Summergrad.

It was edited by Josh Levin, Joel Meyer, and Derek John, Slate’s executive producer of narrative podcasts.

Merritt Jacob is our senior technical director.

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