evidence: - Currently, there are two types of COVID-19 vaccines for use in the United States: mRNA, and protein subunit vaccines. [...] How mRNA COVID-19 vaccines work - First, mRNA COVID-19 vaccines are given in the upper arm muscle or upper thigh, depending on the age of who is getting vaccinated. - After vaccination, the mRNA will enter the muscle cells. Once inside, they use the cells’ machinery to produce a harmless piece of what is called the spike protein. The spike protein is found on the surface of the virus that causes COVID-19. After the protein piece is made, our cells break down the mRNA and remove it, leaving the body as waste.