Immune response to covid-19 vaccine, illustration. Covid-19 is a respiratory disease caused by the SARS-CoV-2 virus (blue, left). mRNA (messenger ribonucleic acid) Covid-19 vaccines contain instructions that tell cells (pink, right) in the body to make and display viral spike proteins (red). The body recognizes these proteins as foreign and initiates the immune response. Antibodies (light blue) are produced against the protein. The body will be able to produce these antibodies quickly in future infections.