The first two vaccines to become available for use — those developed by Pfizer and its German partner, BioNTech, and Moderna — use messenger RNA (mRNA) to instruct the body to build the coronavirus’ signature spike protein. The body then produces antibodies to combat the Coronavirus when it enters the body.

The first dose helps your body create an immune response, while the second dose strengthens your immunity to the virus. The Pfizer-BioNTech vaccine requires two doses given 21 days apart. The Moderna vaccine requires two doses given 28 days apart.