"This is 100 percent wrong," Dr. Bhuyan said. "The flu vaccine cannot cause a cold or the flu, and it's the best way to protect ourselves from the flu." The flu shot contains a strain of virus that has been killed or weakened, which wouldn't leave you feeling ill. If you do feel sick after getting the shot, it's more likely that you were exposed to a virus just before or after being vaccinated. It takes about two weeks for your body to produce the antibodies that help keep you protected from the flu, and the vaccine isn't designed to fend off the common cold. Still haven't gotten your flu shot? It's never too late.