by Sandra Douglas

Created on: September 17, 2010

Vaccines, including flu shots, rarely cause allergic reactions, also known as hypersensitivity reactions. A study done by the Center for Disease Control—Vaccine Safety Datalink, found that from 1991 to 1997, the risk for children to experience a severe allergic reaction following vaccine was 1.5 cases per 1 million vaccines administered.  

The adverse reactions most often reported by people after receiving a flu shot include redness and pain at the injection site. Some complain of a mild fever and fatigue for a day or two following the vaccine, but these are less common. These are the most common adverse reactions but they are not necessarily hypersensitivity reactions. All medications have side effects that occur with varying frequency. A hypersensitivity reaction, also known as an allergic reaction, occurs as the body's response to a foreign protein. An adverse reaction is caused by the medication; a hypersensitivity reaction is caused by the body's response to something in the medication.

Some people misinterpret the common adverse reactions to the flu shot as a form of the flu. It’s important to know that the flu shot cannot give you the flu. Vaccines are made using killed cultures of the virus so they cannot make you sick. They can, however rarely, cause an allergic reaction.

An allergic reaction occurs when the immune system reacts to a protein introduced into the body. This protein is called an antigen. Most people do not react to the antigen but others are more sensitive, or hypersensitive. Their body produces an allergic reaction that may be as mild as itching and hives, or as serious as anaphylactic shock. Allergic reactions develop in as little as 10 minutes or they may not occur for several hours.

Signs of an allergic reaction include itching, redness, or hives anywhere on the body. Hives are raised, reddened, sometimes fluid filled bumps that occur in patches or cover the entire body. A more severe allergic reaction is called anaphylaxis.

Signs of anaphylaxis are:

Swelling of the mouth, tongue or throat. Difficulty breathing, wheezing, coughing, or tightness in the chest. Generalized itching Vomiting Skin may become pale and clammy.  Dizziness, light-headedness, or confusion. Extreme anxiety. Drop in blood pressure.

Anaphylaxis is a life-threatening allergic reaction. Symptoms can progress rapidly. Do not leave the person alone and call 911 immediately.

Anyone who has ever had an allergic reaction to a vaccine or to eggs must be very cautious about taking a vaccine. Vaccines are made using eggs, and tiny amounts of egg protein are in each flu vaccine. Vaccines also contain antimicrobial agents, preservative, stabilizers, any of which may cause an allergic reaction.

Notify your health care professional if you have ever experienced an allergic reaction to eggs or to another vaccine. If the vaccine is necessary, it is still possible for a person with egg allergy to take it; a regimen has been developed to enable children with asthma to safely take the vaccine in spite of a hypersensitivity to eggs. If the doctor decides that the vaccine is safe if given with precautions, be prepared to stay in the office until the danger of an allergic reaction has passed, usually 30 minutes to one hour.

Reference:

http://www.cdc.gov/flu/professionals/acip/adversetiv .htm

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