By the end of 2020, most of the COVID-19 vaccines injected into millions of arms worldwide relied on a technology that had never before been used at this scale in medical history: mRNA. The science behind it was, in fact, the product of a research line that began decades earlier and was repeatedly rejected, nearly abandoned along the way. The story that earned Katalin Karikó and Drew Weissman the 2023 Nobel Prize in Medicine is proof that science sometimes makes its greatest breakthroughs exactly where it meets the most resistance.
How Is It Different From Traditional Vaccines?
Traditional vaccines typically rely on one of two approaches: administering a weakened or inactivated version of the virus, or injecting a protein found on the virus's surface directly. Both methods are slow and complex to manufacture, requiring the virus to be grown in a lab or the protein to be produced in large bioreactors.
mRNA vaccines work on an entirely different principle. Instead of delivering the virus itself or its protein, they send our cells a genetic molecule carrying the instruction: "make this protein yourself." mRNA (messenger RNA) is a molecule that already exists naturally in our cells, carrying information from DNA to the protein-building machinery (ribosomes). The vaccine contains a synthetic mRNA fragment carrying the instructions for the virus's surface protein — for example, SARS-CoV-2's spike protein.
What Happens Inside the Body?
Once injected, the mRNA molecule enters muscle cells and uses the cell's own protein-making machinery to briefly produce the viral protein. The immune system recognizes this foreign protein, produces antibodies against it, and builds immune memory specific to it. Within a few days, the mRNA molecule is naturally broken down and eliminated by the cell — it never integrates into the cell's own DNA or alters the genetic code in any way.
A Decades-Long Story of Rejection
In the 1990s, Katalin Karikó was almost the only researcher at the University of Pennsylvania who believed mRNA could be used therapeutically. The problem was significant: lab-synthesized mRNA triggered a severe inflammatory response in the body and degraded rapidly. Karikó's grant applications were rejected one after another, she failed to get promoted at the university, and at one point was even demoted.
Her meeting with immunologist Drew Weissman in 1997 proved to be the turning point. When the pair replaced one of the nucleoside bases in the mRNA molecule (uridine) with a chemically modified version (pseudouridine), they discovered that the immune system no longer perceived the molecule as a threat — the inflammatory response nearly disappeared. Published in 2005, this finding would later prove to be a turning point in the field, yet it was initially rejected by major scientific journals and received relatively few citations for years.
The Role of Lipid Nanoparticles
For the discovery to become clinically usable, a second technical problem still had to be solved: delivering the fragile mRNA molecule to target cells without it breaking down in the body. That problem was solved through the work of a separate group of researchers who learned to wrap mRNA inside lipid nanoparticles — microscopic, fat-based capsules. These nanoparticles both protected the mRNA from degradation and helped it cross the cell membrane. The combination of pseudouridine modification and lipid nanoparticle delivery formed the technical foundation of the COVID-19 vaccines developed at record speed in 2020.
The Nobel Prize and Beyond
In 2023, Karikó and Weissman were awarded the Nobel Prize in Physiology or Medicine "for their discoveries concerning nucleoside base modifications that enabled the development of effective mRNA vaccines against COVID-19." The Nobel Committee emphasized that the pair's work "addressed one of the most critical needs of humankind during modern times, one of the fastest spreading health crises" in recent memory.
Today, the potential of mRNA technology extends far beyond vaccines. Researchers are using the same platform to develop vaccines against other infectious diseases, including flu, RSV, and Zika. Even more ambitious is the pursuit of personalized cancer vaccines: mRNA molecules designed according to a tumor's specific mutation profile, aiming to train the immune system to recognize and destroy that patient's unique cancer cells. Early-phase clinical trials in certain melanoma and pancreatic cancer types are already showing promising results.
Conclusion
The story of mRNA vaccine technology is a reminder that scientific progress rarely moves in a straight line. Karikó's decades of largely overlooked work became a solution to a global health crisis once it met the right partner at the right time. The cancer vaccines and next-generation vaccines against other infectious diseases now being developed in laboratories suggest that this technology's impact has only just begun.