Research that outlasted decades of neglect
Hungarian-born biochemist Katalin Karikó spent the 1990s at the University of Pennsylvania pursuing mRNA therapies. Her grant applications were rejected again and again, and she was even demoted. Injected mRNA triggered fierce inflammation, so most experts thought it was impractical. In 2005 she and immunologist Drew Weissman found that swapping one building block, uridine, for pseudouridine dramatically reduced that inflammation. Their work fed into BioNTech and Moderna. When COVID-19 struck, the Pfizer–BioNTech vaccine was authorized 11 months after the virus's sequence was published. Karikó and Weissman won the 2023 Nobel Prize in Physiology or Medicine.
How it works
mRNA is the work order that carries genetic instructions from DNA to the cell's protein factories, the ribosomes. The vaccine wraps instructions for the coronavirus spike protein in lipid nanoparticles and injects them into muscle. For a few days, cells make spike proteins and display them. The immune system responds with antibodies and T cells, so it can react quickly to the real virus. The mRNA never enters the nucleus, can't alter DNA, and breaks down within days. Because only the sequence needs changing, a vaccine matched to a new variant can be designed in weeks.
Side effects and the future
Common side effects are a sore arm, fever, and fatigue, which pass in a day or two. Myocarditis has been reported rarely, mostly in young men. Very rarely, anaphylaxis or another hypersensitivity reaction occurs. mRNA vaccines for flu, RSV, and Zika are in development, along with personalized cancer vaccines tailored to a patient's tumor mutations. In 2023 a Moderna–Merck melanoma vaccine cut the risk of recurrence by about 44%. Unlike CRISPR, which edits genes permanently, mRNA only makes a protein for a short time.
FAQ
- Can an mRNA vaccine change my DNA?
- No. mRNA doesn't enter the nucleus and breaks down within days.
- How was it developed so fast?
- Thirty years of groundwork meant only the sequence had to change, and trial phases were run in parallel.
Sources reviewed: 2026-10-26
References
- Karikó, K., Buckstein, M., Ni, H., & Weissman, D. (2005). Suppression of RNA recognition by Toll-like receptors. Immunity, 23(2), 165–175.
- Polack, F. P., et al. (2020). Safety and efficacy of the BNT162b2 mRNA Covid-19 vaccine. NEJM, 383, 2603–2615.
- Nobel Prize in Physiology or Medicine 2023: Karikó & Weissman. NobelPrize.org.