Both mRNA and viral vector vaccines contain instructions that teach our cells how to create "spike proteins", which is the protein found on the surface of the virus that causes COVID-19. Once your cells produces COVID-19 spike proteins, your immune system recognizes that those proteins don’t belong in your body and creates antibodies to stop the virus from spreading and causing damage when you are exposed to it. Neither vaccine contains the virus that causes COVID-19.

The instructions in the mRNA vaccines are messenger RNA (mRNA), the genetic material that tells your cells how to make proteins. The mRNA is surrounded by tiny lipids (fatty molecules) which help mRNA enter directly into your cells. Once your cells create the spike proteins, your body breaks down the mRNA.

In viral vector vaccines, spike protein DNA is placed inside a modified version of a different virus that doesn’t cause illness. This non-harmful virus delivers the DNA instructions to your cells – this virus is called the vector.