Hungarian American biochemist Katalin “Kati” Karikó became fascinated by science as a child and grew up determined to find a way to use messenger RNA―a copy of a part of DNA that provides cells with instructions to make proteins―to help fight illness. An mRNA vaccine had never been made before, and she faced frequent criticism and was told by other scientists she would never succeed. Karikó refused to give up her research, and when the COVID-19 pandemic hit, she played a critical role in developing the successful Pfizer-BioNTech mRNA vaccine faster than any other vaccine in history.