Information You Need: How mRNA vaccines work

With the recent promising news of two mRNA COVID-19 vaccines, Pfizer and Moderna, many people may be wondering more about how this specific vaccine type works. Messenger RNA vaccines, also commonly called “mRNA vaccines,” are a newer, but well understood way to protect our bodies from infectious diseases. 

Other common vaccines, such as the flu shot, inject dead or inactivated flu virus particles to cause an immune response. Instead, mRNA vaccines inject a harmless piece of protein, specifically a “spike protein,” taken from the virus that then provides instructions for our body to make the protein. Our immune system then identifies it triggering an immune response to destroy it. Once the immune system has seen it once, it recognizes the protein on the actual virus and can produce antibodies and other immune cells quickly to destroy it before it becomes a problem. 

Below are some simplified steps to demonstrate how these mRNA vaccines work.

  1. The mRNA vaccine is given as a shot in the upper arm muscle. 
  2. Muscle cells then use the protein-creating instructions provided by the mRNA to make the piece of protein 
  3. The cell breaks down the mRNA instructions after creating the protein piece
  4. The muscle cell then presents the created protein piece on the cell’s surface
  5. Our body’s immune system notices that this is not a usual protein and it begins to make antibodies to mount an immune response to that specific protein. 
  • This process is similar to what happens when our bodies are actually infected with the COVID-19 virus, but since it is not a whole virus it cannot replicate in the body. Vaccines prevent our bodies from getting ill and experiencing serious health effects of the virus.

This process causes an immune response and in some people can cause fatigue, aches, fever, and other symptoms that are limited. This happens more on the second dose. A second dose is needed to have the vaccine be as effective as possible, up to 95%!. Given the long term consequences of infection with the actual virus (lung damage, blood clots, neurological problems), having limited symptoms for a day or two is much less risky. 

For more information you can watch this video segment by Dr. Bhattacharya on mRNA vaccinesor you can visit this CDC link.

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