Katalin Kariko and Drew Weissman

They met in the late 1990s at the copier between their labs at the University of Pennsylvania, and that chance meeting led to a history-making vaccine and a Nobel Prize for both. Dr. Drew Weissman was working on developing an HIV vaccine, and Katalin Kariko was struggling to keep her lab open and convince her superiors that her chosen research topic, the genetic material called RNA, was a promising target for a new generation of treatments. Weissman had been focusing his efforts on a DNA-based vaccine, but was open to new suggestions, and at Kariko’s urging, began collaborating with her on an RNA-based approach. The problem was that while RNA activated the immune system, a plus for a vaccine, it also triggered dangerous inflammation. “We saw the potential of RNA, and neither of us would give up,” Weissman told TIME in 2021. “Maybe it’s stubbornness, maybe it’s stupidity—I’m not sure what the best description is for why we kept working at it for so many years. But we did.” Together the pair eventually came up with a way to stabilize the notoriously fickle RNA and curb its inflammatory properties, and published what they expected to be a widely recognized scientific coup in 2005.

But that recognition didn’t come for another 15 years, in the middle of the COVID-19 pandemic, when researchers realized that their discovery was the key to speeding up development of the first mRNA vaccine against the new virus. In under a year, both Pfizer-BioNTech and Moderna developed mRNA-based COVID-19 vaccines based on Kariko and Weissman’s method. The shots helped to slow the swift transmission of SARS-CoV-2 and earned Kariko—now a research scientist at the University of Szeged in Hungary—and Weissman—who is director of vaccine research at Penn's Perelman School of Medicine—the 2023 Nobel Prize in Physiology or Medicine. And after decades of being dismissed for their focus on RNA, the pair have pioneered a new era of mRNA-focused treatments, for not just infectious diseases but cancer as well.