2. The shot can give you influenza
If you become ill after receiving the flu shot, the immunization isn’t to blame. “After getting an immunization, your body mounts a mini immune response to create the antibodies that you need [to provide protection against the flu],” says Dr. Kerr. “Some people might feel a little sick a day after the shot because their body’s mimicking fighting an infection, but they don’t actually have the flu.” If you have a prolonged bout of coughing or a stuffy nose, a cold virus is usually the culprit. “Some people are sick with a cold around the time that they get a flu shot and think it was caused by the shot, but that’s not the case,” he says.