Celebrating Penn Medicine's
Lifesaving Science
Drew Weissman, MD, PhD & Katalin Karikó, PhD mRNA Vaccine Creators

COVID-19 mRNA Vaccine Pioneers

Katalin Karikó, PhD
& Drew Weissman, MD, PhD

Meet the Brilliant Penn Medicine Minds Behind the mRNA COVID-19 Vaccines

Today's mRNA vaccines for COVID-19 – currently the world’s best hope to end the pandemic – got their start at Penn Medicine. Two Penn researchers, Katalin Karikó, PhD, and Drew Weissman, MD, PhD, invented messenger RNA (mRNA) technology that serves as the foundation of the Pfizer/BioNTech and Moderna vaccines.

Drs. Karikó and Weissman's mRNA discovery opened the floodgates for additional mRNA vaccines with potential to eradicate countless other diseases, even cancer.

They have received the world’s most prestigious prizes for their discovery science efforts, including the Lasker-DeBakey Clinical Medical Research Award, the Breakthrough Prize and the Albany Medical Center Prize in Medicine and Biomedical Research.

How do mRNA Vaccines Work?

A vaccine's goal is to train the body's immune system to defend against disease. Many vaccines use a weakened or dead version of the actual virus to stimulate an immune response. In contrast, mRNA (messenger RNA) vaccines use a genetic code to tell the body's cells to produce proteins that the immune system recognizes as the virus.

Learn the benefits of mRNA technology and how these vaccines are changing the world.

mRNA vaccines are essentially plug and play. We believe you can change the part of the mRNA that encodes a protein, plugging in new code specific to the virus we hope to protect against, and cause one's body to produce proteins that match that virus' proteins. We do not have to develop and manufacture an entirely new formula.

Dr. Drew Weissman
Dr. Drew Weissman

Meet the mRNA Vaccine Creators: Drs. Karikó and Weissman

Dr. Katalin Karikó and Dr. Drew Weissman met while arguing over whose turn it was to use a copy machine. Their chance meeting at the University of Pennsylvania ignited a decades-long collaboration that ultimately fueled the mRNA COVID-19 vaccines protecting millions of people worldwide.

  • Dr. Katalin Karikó

    Katalin Karikó grew up in Kisújszállás, Hungary, in a home with no running water, refrigerator or television. Her father was a butcher, and while her older sister and other children were off playing, young Kati watched him chop animal carcasses.

    She earned a bachelor's degree and PhD at the University of Szeged and worked as a postdoctoral fellow at its Biological Research Center. There she learned of a recently discovered molecule, messenger RNA, which told cells what to do.

    Dr. Karikó worked in a lab in Hungary researching mRNA, and she moved to Philadelphia with her family in 1985. For a dozen years, she conducted laboratory research at Penn, trying to progress her idea of modifying mRNA.

    In 1998 she stood at a University of Pennsylvania Xerox machine, wanting to copy a research paper.

  • Dr. Drew Weissman

    Drew Weissman grew up in Lexington, Massachusetts and is the son of an engineer and dental hygienist. He was always taking things apart so he could put them back together.

    Dr. Weissman received his bachelor's degree and master's degree from Brandeis University, majoring in biochemistry and enzymology. He earned his MD and PhD from Boston University, focusing on immunology and microbiology. Dr. Weissman completed his residency at Beth Israel Hospital.

    He was a fellow at the National Institutes of Health studying HIV in the lab of Dr. Anthony Fauci. He joined the University of Pennsylvania in 1997 to start a lab to study RNA and innate immune system biology.

    In 1998 he stood at a University of Pennsylvania Xerox machine, wanting to copy a research paper.


After a brief exchange over who could use the copier next, Drs. Karikó and Weissman struck up a conversation. He said he was using DNA to make an HIV vaccine. She argued for RNA. Intrigued, he asked her to join his lab.

Dr. Karikó was an expert in RNA but not a physician with immunology expertise. Dr. Weissman was a practicing immunologist but didn't have Dr. Karikó's RNA experience. Their combined backgrounds created a perfect environment for shared understanding and research.

We shared knowledge. We shared papers. We taught each other everything. But by doing that, it allowed us to figure out how to make modified RNA and how to make this vaccine. And I think either of us alone, that would have never happened because we needed both elements, both types of science involved.
- Dr. Weissman

In petri dish experiments, Dr. Karikó’s modified mRNA molecules could instruct cells to make the protein she desired. Her goal was the same when injecting mRNA into mice: New genetic instructions would cause the mice to make a customized protein and elicit an immune response. Unfortunately, the mice experienced harmful inflammation, and some died.

After several more experiments Drs. Karikó and Weissman made a breakthrough. They found that modifying part of the mRNA eliminated inflammation. Also, encapsulating the mRNA in tiny lipid (fat) droplets created molecules that, instead of being cast out by the immune system, worked with it to fight disease.

We kept doing experiments. We kept getting results. We kept getting excited by the results.
- Dr. Weissman

In 2005, Drs. Karikó and Weissman published landmark research that explained how mRNA could be altered for therapeutic use. They also revealed how mRNA can be delivered into the body to reach the proper target. Unfortunately, few scientists paid attention. Undeterred, Drs. Karikó and Weissman persevered.

Then COVID-19 hit, and the modified mRNA technology developed at Penn Medicine by Drs. Karikó and Weissman took center stage. Both Pfizer/BioNTech and Moderna licensed Penn technology, which is used in the vaccines now being deployed to combat the virus.

Dr. Weissman and Dr. Kariko receive mrna vaccine shot at Penn Medicine.

The Pfizer/BioNTech vaccine was the first to receive FDA Emergency Use Authorization (EUA) in December 2020 for those 16 or older, and the first COVID-19 vaccine to receive full vaccine approval for the same age group. In May 2021, the EUA was expanded to include adolescents ages 12 to 15. In August 2021 it was amended again to allow for a third dose for certain people who are immunocompromised. The vaccine remains available under EUA for these groups. Moderna Therapeutics, which was granted EUA for its mRNA COVID-19 vaccine in December 2020, also uses the same modified mRNA technology created at Penn.

To date, a combined 360 million doses of mRNA COVID-19 vaccine have been administered in the U.S. alone. The Pfizer/BioNTech vaccine is protecting people from the disease in 126 countries across the globe, and 71 countries are using the Moderna vaccine.

On December 18, 2020, Drs. Karikó and Weissman received their first doses of the Pfizer/BioNTech COVID-19 mRNA vaccine, more than 20 years after meeting at that copy machine.

Beyond COVID-19, the potential for using modified mRNA to prevent and heal disease are extensive. Read this Q&A with Dr. Weissman about the COVID-19 vaccine and mRNA technology's future applications.

The work of Drs. Weissman and Karikó is the scientific foundation on which these innovative and lifesaving vaccines rest. Their discovery of how to chemically modify mRNA to more effectively produce proteins in vivo laid the groundwork for the rapid development and deployment of mRNA vaccines—and has sparked a completely new way to look at prevention of infectious diseases and novel pathways for the treatment of cancer and other serious conditions.
J. Larry Jameson, MD, PhD
Executive Vice President of the University of Pennsylvania for the Health System
Dean of the Perelman School of Medicine

How Penn Is Using mRNA Vaccine Technology Beyond COVID-19

Drs. Karikó and Weissman's discoveries launched endless possibilities to prevent and treat many diseases. Penn scientists are working to leverage mRNA technology for vaccines to combat:

All coronaviruses

Including SARS (severe acute respiratory syndrome), MERS (Middle East respiratory syndrome) and future variants.

Infectious diseases

Such as influenza, herpes, C. difficile, hepatitis C, HIV, malaria, Lyme disease and norovirus.

Neurodevelopmental disorders

Such as amyotrophic lateral sclerosis (ALS) and dementia.

Genetic conditions

Such as sickle-cell anemia.

Penn Medicine researchers are leaders not only in developing new approaches, vaccines and treatments, but in getting them to patients who need them. For example, Dr. Weissman's team is working with Chulalongkorn University in Thailand to help them produce an mRNA vaccine for preventing COVID-19 in middle-to-low-income countries.

Even before COVID hit, we had already set up clinical trials for mRNA vaccines for genital herpes, influenza, and HIV, and we're developing more pathogen vaccines right now.

Drew Weissman, MD, PhD
Roberts Family Professor in Vaccine Research
Director of Vaccine Research, Division of Infectious Diseases

Global Awards Drs. Karikó and Weissman Have Earned for Their COVID-19 Work

Drs. Karikó and Weissman are earning international prizes and acclaim for their lifesaving discoveries.

Dr. Weissman and Dr. Kariko mRNA vaccine research in Penn Medicine lab.