Why do so many people say the flu shot gives them the flu?

Similar viruses: It is a killed vaccine, so it does not cause viral infection. Most have no side effects except a sore arm , it rarely cause flu like illness. It may just be an excuse not to receive the vaccine, or what others have said. The influenza vaccine is given in the fall and winter months, when many similar viuses, for which no vaccine exists, circulate and cause illnesses.