Scientists have been studying messenger RNA (mRNA) vaccines for more than 20 years. Unlike some types of older vaccines, mRNA vaccines do not use weakened or inactivated viruses. Instead, the mRNA-based COVID-19 vaccines stimulate muscle cells to produce harmless spike proteins found on the outer shell of SARS-CoV-2, the virus that causes COVID-19. These proteins trigger an immune response that teaches your body how to recognize and fight off the virus. These vaccines do not give you COVID-19 or alter your DNA in any way.