The Pfizer-BioNTech COVID-19 Vaccine is a messenger RNA (mRNA) vaccine. The vaccine contains a synthetic, small piece of the SARS-CoV-2 genetic material (mRNA) that instructs cells in the body to make the virus’s distinctive “spike” protein. When vaccinated, the body produces copies of the spike protein, which alone does not cause disease, and the immune system learns to react defensively, producing an immune response against SARS-CoV-2.