Ingeborg Rapoport was 25 when she wrote her doctoral thesis, but she had to wait until Wednesday to defend it before an academic committee—77 years later.

Ms. Rapoport, a 102-year-old retired neonatologist who lives in Berlin, submitted her thesis to the University of Hamburg in 1938, five years after Adolf Hitler took power. Her topic was diphtheria, an infectious disease that was then a leading cause of death among children in the U.S. and Europe.

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