None of the vaccines contain a live COVID-19 virus. The goal of vaccination is to teach the body’s immune system how to recognize and fight the virus that causes COVID-19. Sometimes this process can cause symptoms, such as fever, but these symptoms are normal and are actually a good sign that the body is building immunity.
It typically takes a few weeks for the body to build immunity after vaccination. That means it’s possible a person could be infected with the virus that causes COVID-19 or another virus just before or just after vaccination and get sick.