The Centers for Disease Control, which monitors the vaccine, says reactions are usually mild. They happen soon after getting inoculated and last only one or two days.
The CDC says mild symptoms include soreness, redness, or swelling at the point of injection if you receive the shot.
Fainting, headache, muscle aches, fever, and nausea can also occur.
More serious side effects could be signs of an allergic reaction and include high fever, behavioral changes, difficulty breathing, hoarseness, wheezing, swelling around the eyes or lips, hives, paleness, and a fast heart beat or dizziness.
Since the flu vaccine is grown in chicken eggs, people with an egg allergy should avoid it altogether.