Katalin Karikó and Drew Weissman, who together identified a chemical tweak to messenger RNA that laid the foundation for vaccines against Covid-19 that have since been administered billions of times globally, were awarded the Nobel Prize in Physiology or Medicine on Monday.
Dr. Karikó, the daughter of a butcher in Hungary who became an mRNA specialist, and Dr. Weissman, a physician and virologist searching for an H.I.V. vaccine, met over a copy machine at the University of Pennsylvania in 1998.
Together, their work transformed vaccine technology.
Seven years after their first meeting, they published a surprising finding about messenger RNA, also known as mRNA, which provides instructions to cells to make proteins.
When mRNA was introduced to cells, the molecules were so delicate that the cells instantly destroyed it. But the scientists found that they could avert that outcome by slightly modifying the mRNA. When they added the altered mRNA to cells, it could briefly prompt cells to make any protein they chose.
Up to that point, commercial vaccines had carried modified viruses or pieces of them into the body to train the immune system to attack invading microbes. An mRNA vaccine would instead carry instructions — encoded in mRNA — that would allow the body’s cells to pump out their own viral proteins.
This approach, Dr. Weissman and Dr. Karikó thought, would better mimic a real infection and prompt a more robust immune response than traditional vaccines did.
At the time, scientists were largely uninterested in taking up that new approach to vaccination. Their paper, published in 2005, was summarily rejected by the journals Nature and Science, Dr. Weissman said. The study was eventually accepted by a niche publication called Immunity.
But eventually, two biotech companies took notice of the work: Moderna, in the United States, and BioNTech, in Germany. The companies studied the use of mRNA vaccines for flu, cytomegalovirus and other illnesses, but none moved out of clinical trials for years.
Then the coronavirus emerged. The strikingly effective vaccines made by Moderna and Pfizer-BioNTech use the modification Dr. Karikó and Dr. Weissman discovered.
Dr. Karikó is the 13th woman to be awarded the Nobel Prize in Physiology or Medicine since 1901, and the first since 2015. Women represent a small fraction of the total of 227 people who were awarded the prize, a reflection of how women are still largely underrepresented in the field of science and scientific awards, including the Nobel Prizes.
Women account for less than 7 percent of Nobel laureates, a total that has produced criticism for the institute that awards the prizes.
When will the other Nobel Prizes be announced?
The prize for physiology or medicine is the first of six Nobel Prizes that will be awarded this year. Each award recognizes groundbreaking contributions by an individual or organization in a specific field.
The Nobel Prize in Physics will be awarded on Tuesday by the Royal Swedish Academy of Sciences in Stockholm. Last year, John Clauser, Alain Aspect and Anton Zeilinger each won for independent works exploring quantum weirdness.
The Nobel Prize in Chemistry will be awarded on Wednesday by the Royal Swedish Academy of Sciences in Stockholm. Last year, Carolyn R. Bertozzi, Morten Meldal and K. Barry Sharpless shared the prizes for work on click chemistry.
The Nobel Prize in Literature will be awarded on Thursday by the Swedish Academy in Stockholm. Last year, Annie Ernaux earned the prize for work that dissected the most humiliating, private and scandalous moments from her past with almost clinical precision.
The Nobel Peace Prize will be awarded on Friday by the Norwegian Nobel Institute in Oslo. Last year, the prize was shared by Memorial, a Russian organization; the Center for Civil Liberties in Ukraine; and Ales Bialiatski, a jailed Belarusian activist.
Next week, the Nobel Memorial Prize in Economic Sciences will be awarded on Monday by the Royal Swedish Academy of Sciences in Stockholm. Last year, Ben S. Bernanke, Douglas W. Diamond and Philip H. Dybvig shared the prize for work that helped to reshape how the world understands the relationship between banks and financial crises.
All of the prize announcements will also be streamed live by the Nobel Prize organization.
Emma Bubola contributed reporting.