When she was at graduate school in the 1970s, Dr. Katalin Kariko learned about something that would become a career-defining obsession: mRNA. She believed in the potential of the molecule, but for decades ran up against institutional roadblocks. Then, the coronavirus hit and her obsession would help shield millions from a once-in-a-century pandemic. Today, a conversation with Dr. Kariko about her journey. Guest: Gina Kolata, a reporter covering science and medicine for The New York Times.