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Portrait of Drew Weissman
Photo: Thorne Media at 0:08 and 0:28, cropped, brightened, Breakthrough (Part 1) - 2022 Life Science Medalists, Katalin Karikó and Drew Weissman on Vimeo · CC BY 3.0 via Wikimedia Commons

Nobel Prize in Physiology or Medicine · 2023

Drew Weissman

With Katalin Karikó, he kept lab-made mRNA from setting off the immune alarm, a key step behind mRNA COVID-19 vaccines.

The Nobel citation: “for their discoveries concerning nucleoside base modifications that enabled the development of effective mRNA vaccines against COVID-19”
Born
September 7, 1959, Lexington, MA, USA
Shared with
Katalin Karikó
Affiliation at the time
Penn Institute for RNA Innovations, University of Pennsylvania, USA

Medicine prize

2023

Shared with 1 other laureate.

Age that year

64years

Born in 1959.

Headline credited impact

130,500–1.3 millionlives saved

Deaths averted by mRNA COVID-19 vaccines. How it was built

Sources cited

23

Fact-checked September 24, 2026.

  • He met his research partner Katalin Karikó in the late 1990s while they competed for the same photocopier at the University of Pennsylvania.
  • Nature and Science both turned down the pair's key 2005 paper. It ran in the journal Immunity instead and later won them the Nobel Prize.
  • Both the Pfizer-BioNTech and Moderna COVID-19 vaccines swap one RNA building block for a chemically modified cousin, the trick the pair pioneered.
  • Diagnosed with type 1 diabetes at age five, he says he took things apart so often as a child that the family toaster never worked.
  • After building a facility in Thailand to make vaccines and medicines to clinical standards, he says he helped build 17 more across four continents.

The breakthrough

Modified mRNA that the immune system accepts (2005)

Every cell in your body uses messenger RNA, or mRNA, as a recipe card. It carries instructions from your DNA to the parts of the cell that build proteins. Since the 1980s scientists could make mRNA in a test tube, and some dreamed of injecting it so the body would build its own medicines or vaccine targets. But lab-made mRNA had two big flaws. The immune system treated it as an invader and set off inflammation, and cells made little protein from it. At the University of Pennsylvania, Weissman, an immunologist, and the biochemist Katalin Karikó noticed that some natural RNA from our own cells, especially a type called transfer RNA, did not set off these alarms. That RNA carries many chemically tweaked letters. So they built mRNA in which one letter, uridine, was replaced by a slightly altered version called pseudouridine. In 2005 they showed that the immune sensors that detect RNA largely ignored the modified molecules. In 2008 and 2010 they showed that cells also made much more protein from it. Think of a visitor entering an office building: without a staff badge, security sounds the alarm, but with the right badge the visitor walks straight in and gets to work. The modified letters are the badge. The COVID-19 vaccines later used a close cousin of pseudouridine that works even better. Weissman's lab also helped show that tiny fat bubbles called lipid nanoparticles could carry the mRNA into the body.[2],[3],[13],[14]

“as important as the vaccine is, if you don’t take it, it doesn’t work.”
Drew Weissman, Telephone interview with NobelPrize.org on the morning the prize was announced, 2 October 2023, describing a new group he had helped start to fight vaccine misinformation.[5]

What it meant for humanity

When COVID-19 spread in early 2020, the modified-mRNA method was ready. BioNTech with Pfizer, and Moderna, both used licensed Penn technology to make vaccines from modified mRNA carrying the recipe for the virus's spike protein. Both reported about 95% protection in large trials and were approved in December 2020, within about a year of the outbreak. Because mRNA is made in a test tube rather than grown in cells, the recipe can be changed quickly, and updated shots followed as new variants spread. Pfizer and BioNTech had delivered more than 4.3 billion doses by March 2023, and Moderna delivered about 807 million in 2021 alone, so mRNA vaccines likely made up roughly two of every five of the more than 13 billion COVID-19 doses given worldwide. How many lives all COVID-19 vaccines saved depends on the method. An Imperial College London model put deaths averted in the first year alone at 14.4 million to 19.8 million. A more conservative 2025 study led by Stanford researchers estimated about 2.5 million through late 2024, 90% of them people aged 60 or older. Either way, the mRNA vaccines' part runs from hundreds of thousands to millions of lives. The same approach is now being tested against cancer and other diseases. Weissman has also worked on access: he has run a lab in Thailand for about 30 years and one in Botswana for about 25, and has helped build vaccine production sites in several regions so local scientists can make their own medicines.

  • The two modified-mRNA COVID-19 vaccines showed about 95% and 94% protection in trials and were approved in December 2020, within about a year of the outbreak.[2],[3]
  • An Imperial College London model estimated that COVID-19 vaccines of all types prevented 14.4 million to 19.8 million deaths in their first year of use.[16]
  • A more conservative 2025 study estimated about 2.5 million lives saved by COVID-19 vaccines through late 2024 (range 1.4 to 4.0 million), 90% of them people aged 60 or older.[17]
  • Pfizer and BioNTech delivered more than 4.3 billion doses of their mRNA vaccine by March 2023; in the US alone, more than 655 million mRNA doses had been given by October 2023.[12],[18]
  • Weissman has run research labs in Thailand and Botswana for decades, training local scientists to make vaccines and RNA medicines themselves.[4]

Impact in numbers

Weissman's contribution was a key that opened a whole platform. With Karikó he found how to make lab-made mRNA quiet enough for the immune system and productive enough for cells, and that finding sits inside both mRNA COVID-19 vaccines. We credit him with 15% of the lives saved by mRNA COVID-19 vaccines, and the same share of the rare heart-inflammation cases they caused. The rest belongs to Karikó, who shares the discovery equally, and to the other essential steps: lipid nanoparticle delivery, the stabilized spike design, company development and public funding. The range is wide because experts disagree on how many lives the vaccines saved. Some value resists counting: vaccines helped societies reopen, and the world now has a vaccine platform that can be redesigned quickly for new threats. Uses in cancer, gene therapy and other infections are still in trials and are not counted here.

HealthFundamental science

Each number is the laureate’s credited share of a real-world outcome, cumulative to 2025. The whole outcome, the share of credit, and the reasoning are shown so you can check the arithmetic. Outcomes shared with other laureates are counted once on the impact page.

  • Medium confidenceDirectModeledHealth

    Deaths averted by mRNA COVID-19 vaccines

    130,500–1.3 million

    lives saved, credited share

    That is 15% of 870,000–8.9 million lives saved since 2020.

    How this number was built

    All COVID-19 vaccines: Ioannidis et al. (2025) estimate 2.5M deaths averted Dec 2020-Oct 2024 (sensitivity 1.4-4.0M; 1 per 5,400 doses, implying about 13.5B doses); Watson et al. (2022) estimate 14.4M (reported deaths) to 19.8M (excess deaths) in the first year alone. mRNA share of doses: Pfizer-BioNTech's 4.3B delivered by Mar 2023 plus Moderna's 0.81B in 2021 = about 5.1B of about 13.5B, about 38%. Low = 2.5M x 35% = 0.87M. High = 19.8M x 45% = 8.9M (upper share allows for Moderna's uncounted post-2021 doses and heavy mRNA use among older people). Share 0.15: the Nobel committee calls the base modification a turning point, but lipid nanoparticle delivery, the stabilized spike, the improved m1-pseudouridine base, industry and public funding were also essential; Karikó and Weissman together get 0.3, split equally.[2],[3],[16],[17],[18],[19]

    Sources: JAMA Health Forum (via PubMed); The Lancet Infectious Diseases (via PubMed); Pfizer Inc.; U.S. Securities and Exchange Commission (EDGAR); The Nobel Assembly at Karolinska Institutet (NobelPrize.org); The Nobel Committee for Physiology or Medicine (NobelPrize.org)

  • HarmLow confidenceDirectModeledHealth

    Myocarditis cases linked to mRNA COVID-19 vaccines

    3,000–10,500

    people harmed, credited share

    That is 15% of 20,000–70,000 people harmed since 2020.

    How this number was built

    Oster et al. (2022): 1,626 confirmed cases after 354.1M US mRNA doses = 0.46 per 100,000 doses (passive reporting, likely an undercount). Mevorach et al. (2021), Israeli active surveillance: 136 definite or probable cases among about 5.1M two-dose recipients (at least 10.2M doses) = about 1.3 per 100,000 doses. Applied to about 5.1B mRNA doses (Pfizer-BioNTech 4.3B by Mar 2023 + Moderna 0.81B in 2021): low 5.1B x 0.46/100k = 23,000, rounded down to 20,000 because later boosters carried lower risk and not every shipped dose was used; high 5.1B x 1.3/100k = 66,000, rounded up to 70,000 for doses given after these tallies. Most cases were mild (95% in Israel). Share 0.15, matching the benefit claim.[18],[19],[20],[21]

    Sources: JAMA (via PubMed); New England Journal of Medicine (via PubMed); Pfizer Inc.; U.S. Securities and Exchange Commission (EDGAR)

The double edge

Safety systems in many countries tracked the mRNA COVID-19 vaccines closely, and serious side effects have been rare, but not zero. The clearest risk is myocarditis, an inflammation of the heart muscle, seen mostly in teenage boys and young men within days of a second dose. Most cases were mild and got better, but some were serious, and at least one in Israel was fatal. A second problem was access: in 2021 poorer countries could not get enough vaccine, and one modeling study estimated that many more lives in low-income countries could have been saved if vaccination targets had been met. Weissman, Karikó and Penn also earn money from licenses on the technology, which Penn discloses.

  • Moderate

    Rare heart inflammation after vaccination

    US safety monitoring confirmed 1,626 myocarditis cases after 354 million mRNA doses from December 2020 to August 2021. Rates were highest after the second dose in boys aged 16 to 17, about 106 cases per million Pfizer-BioNTech doses. Among patients under 30, most had recovered from their symptoms by hospital discharge; in an Israeli review, 95% of cases were mild and one was fatal.[20],[21]

  • Moderate

    Unequal access in poorer countries

    Vaccine shortfalls meant low-income countries missed early coverage targets. A modeling study estimated that meeting the 20% coverage target set by the COVAX program would have averted about 45% more deaths in low-income countries during the first year.[16]

  • Minor

    Financial stake in the vaccines

    Both mRNA COVID-19 vaccines use technology licensed from the University of Pennsylvania. Penn states that it, Karikó and Weissman have received significant financial benefits from these sales, and that BioNTech funds some of Weissman's research.[12]

Against the odds

Weissman grew up in a very different America from the one earlier generations of Jewish scientists faced. He studied at Brandeis, a university American Jews founded in 1948, when many colleges still discriminated against Jewish applicants, other minorities and women. Published profiles of Weissman do not describe him facing antisemitism himself. His hurdles were of other kinds. At age five he was diagnosed with type 1 diabetes, at a time when, as he later learned, children with the disease were not expected to live a full life. As a scientist he spent years on an idea few others valued. He has described two decades with no funding and journals that would not publish their papers, and Nature and Science both rejected the key 2005 study. Once the vaccines arrived, they became targets of conspiracy theories. In Europe, some anti-vaccine activists recycled old antisemitic myths, claiming a Jewish elite was behind the pandemic and profiting from it, and some protesters trivialized the Holocaust by wearing copies of the Nazi-era yellow star marked 'unvaccinated'.

  • —

    Other

    Diagnosed with type 1 diabetes at age five, when, he later learned, children with the disease were not expected to live a full life.[4]

  • 2005

    Other

    Weissman has said he and Karikó went 20-plus years without funding while journals turned down their papers. Nature and Science rejected their key 2005 paper, and it took more than a decade for the finding to be widely taken up.[8],[15]

  • 2021

    Other

    As the mRNA vaccines rolled out, anti-vaccine groups in Europe spread antisemitic conspiracy theories claiming a Jewish elite was behind the pandemic and profiting from vaccines.[22]

Jewish background

Jewish fatherCulturally Jewish

Weissman was born to a Jewish father, Hal, and a mother of Italian background, Adele, who did not convert to Judaism. The family was not religious, but he grew up celebrating all the Jewish holidays. He married Mary Ellen, who was raised observant, and they kept the holidays with their children, who went to Hebrew school at Temple Beth Hillel-Beth El, a Conservative synagogue near Philadelphia. Asked about his own beliefs, he has said his outlook is closer to Daoism, with nature at its center. When he won the Nobel, Jewish news outlets in the US and Israel covered his Jewish background.[7],[8],[9],[23]

Key dates

  1. September 7, 1959

    Born in Lexington, Massachusetts, to a Jewish father and a mother of Italian background.[1],[7],[23]

  2. 1981

    Earns bachelor's and master's degrees at Brandeis, a university founded by American Jews in 1948, working in Gerald Fasman's biochemistry lab.[8],[10],[11]

  3. 1987

    Earns MD and PhD degrees in immunology and microbiology at Boston University; later trains under Anthony Fauci at the NIH studying HIV.[2],[3],[9]

  4. 1997

    Starts his own lab at the University of Pennsylvania and soon meets Katalin Karikó at the photocopier.[2],[12],[13]

  5. 2005

    With Karikó, shows that mRNA built with modified letters no longer sets off the immune alarm; the paper appears in Immunity.[2],[14]

  6. 2008

    The pair show that pseudouridine-modified mRNA also makes cells produce much more protein.[2],[13]

  7. 2015

    A postdoctoral fellow in his lab, Norbert Pardi, shows the promise of lipid nanoparticles for carrying mRNA into the body.[13]

  8. December 2020

    The Pfizer-BioNTech and Moderna COVID-19 vaccines, both built on modified mRNA, are approved.[2],[3]

  9. 2021

    Shares the Lasker-DeBakey Clinical Medical Research Award with Karikó.[13]

  10. October 2, 2023

    Awarded the Nobel Prize in Physiology or Medicine with Katalin Karikó.[1],[2]

  11. December 7, 2023

    Gives his Nobel lecture, on nucleoside-modified mRNA therapeutics, at Karolinska Institutet in Stockholm.[6]

Sources

  1. 1.Drew Weissman - Facts - 2023 · NobelPrize.org (Nobel Prize Outreach), 2023
  2. 2.Press release: The Nobel Prize in Physiology or Medicine 2023 · The Nobel Assembly at Karolinska Institutet (NobelPrize.org), 2023
  3. 3.Scientific background 2023: Discoveries concerning nucleoside base modifications that enabled the development of effective mRNA vaccines against COVID-19 · The Nobel Committee for Physiology or Medicine (NobelPrize.org), 2023
  4. 4.Transcript from an interview with Drew Weissman (6 December 2023) · NobelPrize.org, 2023
  5. 5.Drew Weissman - Interview (first reactions, telephone interview, October 2023) · NobelPrize.org, 2023
  6. 6.Drew Weissman - Nobel Prize lecture: Nucleoside Modified mRNA-LNP Therapeutics · NobelPrize.org, 2023
  7. 7.Drew Weissman, Katalin Karikó win Nobel in medicine for enabling mRNA COVID vaccines · The Times of Israel, 2023
  8. 8.Penn Professor 'Saves the World' with COVID Vaccine Research (Sasha Rogelberg) · Philadelphia Jewish Exponent, 2021
  9. 9.Drew Weissman, Jewish immunologist, wins Nobel Prize for his work on COVID vaccines (Philissa Cramer) · Jewish Telegraphic Agency, 2023
  10. 10.The Brandeis alum whose research may lead to a COVID-19 vaccine · BrandeisNOW, Brandeis University, 2020
  11. 11.Our Story (history of Brandeis University) · Brandeis University
  12. 12.Katalin Karikó and Drew Weissman, Penn's historic mRNA vaccine research team, win 2023 Nobel Prize · Penn Medicine News, 2023
  13. 13.2021 Lasker~DeBakey Clinical Medical Research Award: Modified mRNA vaccines · Lasker Foundation, 2021
  14. 14.Suppression of RNA recognition by Toll-like receptors: the impact of nucleoside modification and the evolutionary origin of RNA (Karikó, Buckstein, Ni, Weissman), Immunity 23:165-175 · Immunity (via PubMed), 2005
  15. 15.From rejection to the Nobel Prize: Karikó and Weissman's pioneering work on mRNA vaccines (Amit Bansal) · Frontiers in Immunology (via PubMed Central), 2023
  16. 16.Global impact of the first year of COVID-19 vaccination: a mathematical modelling study (Watson et al.) · The Lancet Infectious Diseases (via PubMed), 2022
  17. 17.Global Estimates of Lives and Life-Years Saved by COVID-19 Vaccination During 2020-2024 (Ioannidis et al.) · JAMA Health Forum (via PubMed), 2025
  18. 18.Pfizer-BioNTech COVID-19 Vaccine: U.S. Manufacturing and Distribution Fact Sheet (March 2023) · Pfizer Inc., 2023
  19. 19.Moderna, Inc. Form 8-K (January 2022): 2021 COVID-19 vaccine deliveries · U.S. Securities and Exchange Commission (EDGAR), 2022
  20. 20.Myocarditis Cases Reported After mRNA-Based COVID-19 Vaccination in the US From December 2020 to August 2021 (Oster et al.) · JAMA (via PubMed), 2022
  21. 21.Myocarditis after BNT162b2 mRNA Vaccine against Covid-19 in Israel (Mevorach et al.) · New England Journal of Medicine (via PubMed), 2021
  22. 22.Antisemitism and anti-vax discourse in Europe: A report on conspiracy ideologies and anti-Jewish hatred on Facebook and Twitter · Media Diversity Institute (Get The Trolls Out! project), 2021
  23. 23.This Nobel Prize winner's call to his parents has gone viral. But they always thought he could win it. (Caitlin O'Kane) · CBS News, 2023

Fact-checked on September 24, 2026 by a separate AI fact-checking pass that re-opened the sources, with 13 corrections made. How we check

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