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What is an mRNA Vaccine?


René F. Najera, DrPH

July 29, 2020

With news that an mRNA vaccine against the novel coronavirus causing the current COVID-19 pandemic is going into Phase III clinical trials, many people have been emailing us asking what an mRNA vaccine is and isn't. Here is a quick video by Norbert Pardi, PhD, at the University of Pennsylvania. The video is about 8 minutes long and somewhat technical.

What mRNA vaccines boil down to is this:

  • Your cell needs to create a protein. In this case, that protein is an antibody that will attach itself to the virus and prevent it from infecting other cells or tag it for destruction by your immune system.
  • To make that protein, your DNA in the nucleus of your cell sends code to another part of your cell called a ribosome. That code gives the ribosomes all the instructions they need to gather amino acids and bind them together to make proteins.
  • Under normal circumstances, your immune system would have to “see” the virus, absorb it, have its genetic material “analyzed” by your cells, and then your cells would create the antibodies. This process can take some time, and it requires you to be infected with the virus or vaccinated with a vaccine that contains some or all of the virus.
  • When you are given an mRNA vaccine, the mRNA goes to your immune cell's ribosomes and tells them to create the virus antigen (identifying protein). That antigen would then be recognized by your immune system, and the cells of the immune system would create the antibodies you need to fight off the virus.
  • This skips the need for you to be infected, and the immune cells to find the virus, process it, and present the viral antigens to your immune system.

These vaccines have the advantage that scientists are not growing the virus in the lab, which has been a hindrance sometimes to create enough virus or viral particles to give in a vaccine. The vaccine is not infectious, meaning that the chance of it giving you the disease is zero. And the vaccine has a very low risk of triggering an unwanted immune reaction, since it is nothing more than a blueprint for ribosomes to make proteins (something they do all day long).

The New York Times has a daily-updated vaccine tracker that allows readers to see where different vaccine trials are in their phases of testing, and it also includes some primers on how the different vaccine technologies work. Check it out at:


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