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LONDON — Two pioneers of mRNA research — the technology that helped the world tame the virus behind the Covid-19 pandemic — won the 2023 Nobel Prize in medicine or physiology on Monday.

Overcoming a lack of broader interest in their work and scientific challenges, Katalin Karikó and Drew Weissman made key discoveries about messenger RNA that enabled scientific teams to start developing the tool into therapies, immunizations, and — as the pandemic spread in 2020 — vaccines targeting the SARS-CoV-2 coronavirus. Moderna and the Pfizer-BioNTech partnership unveiled their mRNA-based Covid-19 shots in record time thanks to the foundational work of Karikó and Weissman, helping save millions of lives.


Karikó, a biochemist, and Weissman, an immunologist, performed their world-changing research on the interaction between mRNA and the immune system at the University of Pennsylvania, where Weissman, 64, remains a professor in vaccine research. Karikó, 68, who later went to work at BioNTech, is now a professor at Szeged University in her native Hungary, and is an adjunct professor at Penn’s Perelman School of Medicine. 

The duo will receive 11 million Swedish kronor, or just over $1 million. Their names are added to a list of medicine or physiology Nobel winners that prior to this year included 213 men and 12 women.

The award was announced by Thomas Perlmann, secretary general of Nobel Assembly, in Stockholm. Perlmann said he had spoken to both laureates, describing them as grateful and surprised even though the pair has won numerous awards seen as precursors and had been tipped as likely Nobel recipients at some point.


When Karikó and Weissman were notified on Monday, they both thought it was a prank, possibly from some anti-vaxxer. “This can’t be real,” Weissman recalled at a press briefing organized by Penn. He opted to go back to bed and wait for the announcement with his wife. “And then the press conference starts and it was real. So then we really became excited.”

Every year, the committee considers hundreds of nominations from former Nobel laureates, medical school deans, and prominent scientists from fields including microbiology, immunology, and oncology. Members try to identify a discovery that has altered scientists’ understanding of a subject. And according to the criteria laid out in Alfred Nobel’s will, that paradigm-shifting discovery also has to have benefited humankind.

The Nobel committee framed Karikó and Weissman’s work as a prime example of complementary expertise, with Karikó focused on RNA-based therapies and Weissman bringing a deep knowledge about immune responses to vaccines.

But it was not an easy road for the scientists. Karikó encountered rejection after rejection in the 1990s while applying for grants. She was even demoted while working at Penn, as she toiled away on the lower rungs of academia.

But the scientists persisted, and made a monumental discovery published in 2005 based on simply swapping out some of the components of mRNA.

With instructions from DNA, our cells make strands of mRNA that are then “read” to make proteins. The idea underlying an mRNA vaccine then is to take a piece of mRNA from a pathogen and slip it into our bodies. The mRNA will lead to the production of a protein from the virus, which our bodies learn to recognize and fight should we encounter it again in the form of the actual virus.

It’s an idea that goes back to the 1980s, as scientific advances allowed researchers to make mRNA easily in their labs. But there was a problem: The synthetic mRNA not only produced smaller amounts of protein than the natural version in our cells, it also elicited a potentially dangerous inflammatory immune response, and was often destroyed before it could reach target cells.

Karikó and Weissman’s breakthrough focused on how to overcome that problem. mRNA is made up of four nucleosides, or “letters”: A, U, G, and C. But the version our bodies make includes some nucleosides that are chemically modified — something the synthetic version didn’t, at least until Karikó and Weissman came along. They showed that subbing out some of the building blocks for modified versions allowed their strands of mRNA to sneak past the body’s immune defenses.

While the research did not gain wide attention at the time, it did catch the attention of scientists who would go on to found Moderna and BioNTech. And now, nearly 20 years later, billions of doses of mRNA vaccines have been administered.

“And this,” Weissman said, referring to the Nobel Prize, “has just given RNA the recognition.”

“We are not working for any kind of award,” Karikó said Monday at the press briefing. “The importance was to have a product which is helpful.”

For now, the only authorized mRNA products are the Covid-19 shots. But academic researchers and companies are exploring the technology as a potential therapeutic platform for an array of diseases and are using it to develop cancer vaccines as well as immunizations against other infectious diseases, from flu to mpox to HIV. An mRNA vaccine is highly adaptable compared to earlier methods, which makes it easier to alter the underlying recipe of the shot to keep up with viral evolution.

As she gained global fame, Karikó has been open about the barriers she encountered in her scientific career, which raised broader issues about the challenges women and immigrants can face in academia. But she’s said she always believed in the potential of her RNA research.

“I thought of going somewhere else, or doing something else,” Karikó told STAT in 2020, recalling the moment she was demoted. “I also thought maybe I’m not good enough, not smart enough. I tried to imagine: Everything is here, and I just have to do better experiments.”

To future scientists, Karikó said Monday, “If you like to follow instruction maybe the military [is] the best. If you want to be rich, I don’t know the answer for that. But if you would like to solve problems then, you know science is for you.”

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