General questions

How do mRNA vaccines, like Pfizer-BioNTech and Moderna COVID-19 vaccines, work?


COVID-19 mRNA vaccines instruct our cells to make a harmless piece of what is called the “spike protein.” The spike protein is found on the surface of the virus that causes COVID-19. COVID-19 mRNA vaccines are given in the upper arm muscle. Once the instructions (mRNA) are inside the muscle cells, the cells use them to make the protein piece. After the protein piece is made, the cell breaks down the instructions and gets rid of them. Next, the cell displays the protein piece on its surface. Our immune systems recognize that the protein doesn’t belong there and begin building an immune response by making antibodies, just like what would happen if we were naturally infected with the virus that causes COVID-19.

At the end of the process, our bodies have learned how to protect against future infection. The benefit of mRNA vaccines, like all vaccines, is that vaccinated people gain this protection without ever having to risk the serious consequences of getting sick with COVID-19.

The vaccine cannot give someone COVID-19, because mRNA vaccines do not use the live virus that causes COVID-19. They also do not affect or interact with our DNA in any way.

mRNA vaccines:

  • instruct a person’s cells to make the COVID-19 spike protein, which triggers an immune response
  • cannot give someone COVID-19
  • cannot affect their DNA.