Some people may get flu-like symptoms for a few days after the vaccine and think that they are getting the flu, but that is your body building up the antibodies to learn how to fight the virus if in the event you are infected. Some people experience varying levels of these symptoms, or none at all. Every person is different. If you did get sick after getting the vaccine, it's most likely you were incubating the illness before the vaccine could take effect. Or, it was a different kind of respiratory illness caused by another virus or bacteria, and not the influenza virus.