Pfizer + Moderna mRNA Vaccines : How Do They Work?

The Pfizer and Moderna mRNA vaccines are likely to be the first approved for use against COVID-19, but do you know how they work?

Here is a quick primer on the new mRNA vaccine technology, and how it teaches our body to fight against COVID-19!


Pfizer + Moderna mRNA Vaccines : How Do They Work?

Both Pfizer and Moderna COVID-19 vaccines are based on new mRNA (messenger RNA) technology.

Unlike more traditional methods of using dead particles, or attenuated viruses; an mRNA vaccine does not come with the parts necessary to trigger the immune response.

Instead, the Pfizer and Moderna mRNA vaccines contain mRNA strands – literally coding instructions for our cells.

They are used by our cells to create a protein antigen. Think of it as a flag that tells our body how to identify a particular enemy.

It is this antigen (flag) that triggers the immune response that teaches our body how to fight the real disease.


Pfizer + Moderna mRNA Vaccines : How Do They Prevent COVID-19?

Pfizer-Biontech and Moderna have mRNA-based COVID-19 vaccines that have cleared Stage 3 trials with 95% efficacy rates.

Both rely on mRNA instructions that code for the SARS-CoV-2 spike protein. This spike protein serves as the antigen – a flag that lets our body identify the actual SARS-CoV-2 virus.

The mRNA strands in the Pfizer and Moderna COVID-19 vaccines are used by ribosomes in our cells to create the spike proteins, and then discarded.

The spike protein – flag – is presented on the surface of the cell, triggering the body’s immune response. Think of it as using your cells to create and wave the enemy’s flag.

Our body then learns to create antibodies that target the spike protein. If we actually get infected by SARS-CoV-2, those antibodies will immediately attach to the virus particles :

  • preventing them from infecting our cells
  • cause the virus particles to stick together (agglutinate), making them easier targets
  • identifying the virus particles as targets for phagocytic cells to destroy

The immune response to the spike proteins will also train memory cells, so that they can respond to a future COVID-19 infection weeks or months after vaccination.


COVID-19 mRNA Vaccines : Some Common Myths

We would like to take this opportunity to debunk certain myths about mRNA vaccines, specifically those being developed for use against COVID-19.

False Claim #1 : mRNA Vaccines Can Cause COVID-19

Unlike vaccines using attenuated viruses, mRNA vaccines do not contain any live virus. Therefore, they can never cause COVID-19.

They only contain mRNA instructions to build the identifying features of the SARS-CoV-2 virus – its spike protein.

The immune response to this spike protein may cause COVID-19-like effects (fever, headache, chills, etc.) but that is only your body learning to fight against it.

False Claim #2 : mRNA Vaccines Can Change Our DNA

mRNA strands are read and used only by ribosomes in the cytoplasm of our cells.

They do NOT enter the cell nucleus, which is where our chromosomes (containing our DNA) reside. Therefore, it is not possible for mRNA to change our DNA.

It is also expensive to create these mRNA sequences, so there is just enough in the vaccine to trigger the immune response. There is not enough to saturate our body and change our DNA, even if it’s possible to do it.

False Claim #3 : mRNA Vaccines Stay In Our Cells Forever

mRNA sequences are basically instructions by our DNA to the ribosomes, instructing them to create proteins for the cell to use.

Because the cell’s requirements can change rapidly according to conditions, mRNA are, by nature, short-lived and degrade over time.

That’s why the COVID-19 vaccines from Pfizer-Biontech and Moderna have a short shelf life, and require very low storage temperatures.

They also discarded after use, just like how you discard your shopping list after you are done buying your groceries.

Once they are used by our ribosomes to create the spike proteins, they are discarded by the cell. There is simply no way for mRNA strands to survive long in our body, or our cells.


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Dr. Adrian Wong has been writing about tech and science since 1997, even publishing a book with Prentice Hall called Breaking Through The BIOS Barrier (ISBN 978-0131455368) while in medical school.

He continues to devote countless hours every day writing about tech, medicine and science, in his pursuit of facts in a post-truth world.


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