What Are Reactions to Flu Shot?

Flu shots contain deactivated, or killed, flu viruses. For the 2010-2011 flu season, the U.S. Centers for Disease Control and Prevention, or CDC, recommends that everyone over the age of 6 months be vaccinated against the flu. The trivalent vaccine for this season contains the H1N1 virus that triggered the 2009 flu epidemic, a strain of influenza B and an H3N2 virus. While flu shots are generally safe, some people have significant allergic and other reactions to the injection.


Some people experience localized symptoms at the injection site, while others have negative responses to an injection of any kind. Body-wide symptoms such as fever and muscle aches may appear after flu shots. Some individuals develop respiratory symptoms such as a cough. Patients with a severe allergy to eggs may develop a life-threatening allergic reaction called anaphylaxis.


According to the CDC, some individuals experience swelling, itching, redness or soreness at the injection site. Children and teens are especially prone to fainting right after receiving the shot, says Flu.gov. Muscle aches can affect any part of the body, but don't typically cause severe pain. Anaphylaxis may begin with hives, itching and facial swelling, but quickly leads to respiratory and cardiac collapse.

Time Frame

Fainting is a transient response to an injection and resolves on its own. Injection site reactions, muscles aches and fever typically last only a day or two after the injection, according to the CDC. Anaphylaxis can begin within minutes or hours after the flu shot, and it progresses rapidly from that point.


Localized skin reactions respond well to cool, moist compresses and over-the-counter medications such as acetaminophen or ibuprofen, says Consumer Reports. Individuals who faint should be placed in a supine position with their legs elevated until they regain consciousness, advises Flu.gov. People who have had severe allergic reactions to eggs, or to influenza vaccines in previous years, should not receive the 2010-2011 flu vaccine, says the CDC.


Back in 1976, another deactivated flu vaccine developed to prevent another form of the swine flu was associated with a serious neurological disorder called Guillain-Barre Syndrome. Although more recent flu vaccines have not been linked to this disorder, patients should report any muscle weakness or paralysis immediately to their physicians.

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