The Nobel Prize in Physiology or Medicine has been awarded to a pair of scientists who developed the technology that led to the mRNA Covid vaccines.
Prof Katalin Kariko and Prof Drew Weissman will share the prize.
The technology was experimental before the pandemic, but has now been given to millions of people around the world.
The same mRNA technology is now being researched for other diseases, including cancer.
The Nobel Prize Committee said: "The laureates contributed to the unprecedented rate of vaccine development during one of the greatest threats to human health in modern times."
Both were told they had won by telephone this morning and were said to be "overwhelmed".
Vaccines train the immune system to recognise and fight threats such as viruses or bacteria.
Traditional vaccine technology has been based on dead or weakened versions of the original virus or bacterium - or by using fragments of the infectious agent.
In contrast, mRNA vaccines used a completely differently approach.
During the Covid pandemic, the Moderna and Pfizer/BioNTech vaccines were both based on mRNA technology.
Drs Kariko and Weissman met in the early 1990s when they were working at the University of Pennsylvania, in the United States, when their interest in mRNA was seen as a scientific backwater.
RNA technology works like a translator in the human body.
It converts the language of DNA from a set of genetic instructions into the actual proteins that build and run our bodies.
The idea behind mRNA vaccines is to sneak into that process. If you can develop mRNA that produces parts of a virus or another infection, then those foreign proteins will be built by the body and the immune system will learn how to fight them.
There were problems in the early stages. But by refining the technology, the researchers were able to produce large amounts of the intended protein without causing dangerous levels of inflammation that had been seen in animal experiments.
This paved the way for developing the vaccine technology in people.
During Covid, mRNA vaccines were made to produce Covid's "spike protein".
Katalin Kariko is now a professor at Szeged University in Hungary and Drew Weissman is still working as a professor at the University of Pennsylvania.
