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Allergic Reactions to Flu Shot

The flu shot is an injected vaccine that prevents a person from getting the most-common strains of seasonal influenza. Reactions to the shot are rare, but for some people, especially children who are receiving the shot for the first time, a reaction may occur. Here's what to look for if you suspect a reaction.

  1. Local Reaction

    • A local reaction at the injection site is somewhat common, especially among children. You may see some swelling and redness, and there may be a bit of pain and soreness associated with it. This reaction will begin shortly after the shot is given, is mild and lasts for about 48 hours.

    Systemic Reaction

    • Some people may have some systemic reactions such as fever, fatigue, muscle aches and generally just not feeling well. These symptoms will show up between six and 12 hours after the injection, and will usually only last 24-to-48 hours.

    Serious Allergic Reaction

    • Very rarely does a person develop a severe allergic reaction to the flu shot. Signs of an allergic reaction include difficulty breathing, hives, weakness, dizziness and a racing heartbeat. This reaction will occur very soon, within hours of having the injection. If you are allergic to eggs or have had allergic reactions to eggs in the past, you should speak with your doctor before receiving the flu shot because the virus used for the shot is grown in hens' eggs.

    Guillain-Barré Syndrome

    • Another rare reaction to the flu shot is an illness called Guillain-Barré syndrome. The symptoms of this illness are fever, muscle weakness and nerve damage. Very rarely, paralysis could also occur. The syndrome is normally triggered by an infection that causes the body to damage its own nerves. Only about 1 in 100,000 who receive the flu shot will develop the syndrome.

    What to Do About a Reaction

    • If you have a serious reaction to the flu vaccination, you should immediately call your doctor, or visit the emergency room if it is a very severe reaction. Let your doctor know the exact date and time that you had your flu shot. The health-care provider should also call to file a Vaccine Adverse Event Reporting System (VAERS) form.

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