evidence: The mRNA (Moderna and Pfizer) vaccines do not contain live virus. Each of these contain a single gene from the virus that causes COVID-19. The gene instructs our cells to make the protein, but no other proteins from the virus are made, so whole virus particles are never present. In this manner, people who were vaccinated cannot shed, or spread, the virus to other people as a result of vaccination. If, however, the individual subsequently becomes infected, they can spread the virus during the days before and early during their infection. Of note, the amount of virus shed by vaccinated people quickly decreases, so they generally shed less virus overall compared to unvaccinated, infected individuals. This is also the case for the J&J/Janssen vaccine; however, that version is no longer available in the U.S. [...] Vaccinated people do not shed virus following vaccination. COVID-19 vaccines do not contain live viruses, nor do they cause production of whole viral particles. As such, there is no infectious virus to spread from a vaccinated person to someone else. But a vaccinated person can still be infected and potentially spread the virus to others. If they do not have symptoms, they may spread the virus without even knowing they are infected. While vaccinated individuals who become infected can be a source of viral spread, they do not appear to spread as much virus as unvaccinated individuals who become infected because their immune response is able to respond to the infection more quickly – shortening the length of infection and, therefore, the amount of virus produced.