Although rare, adults can have a bad reaction to a flu shot or the flu nasal spray. If a patient is going to have a bad reaction, it usually happens within a couple hours of getting the shot or nasal spray, per the United States Centers for Disease Control and Prevention.
Some of the signs of a bad reaction include hives, swelling around the eyes, difficulty breathing, dizziness or a high fever, states the CDC. If a patient experiences any of these side effects, it is advised they seek medical attention as soon as possible. If someone has ever had a severe reaction to the flu shot or nasal spray before, they should not receive the vaccination again.