Vaccine allergy

Patients may develop an allergic reaction to a vaccine if the immune system overreacts to substances contained in the vaccine. Most allergic reactions occur when the vaccine contains antibiotics, egg proteins, gelatin, or mercury.

Typically, an allergic response is not triggered the first time the body encounters the allergen (substance that causes an allergic reaction). In fact, some people can be exposed to the allergen several times before an allergy develops. It is only after one or more episodes of exposure to an allergen that the immune system becomes sensitized. During this process, the body's white blood cells develop immunoglobulin E (IgE) antibodies to the allergens. Once sensitized, the antibodies quickly detect and bind to the allergens in the body.

After binding to allergens, antibodies trigger other immune cells to release chemicals (such as histamine) that cause allergic symptoms, such as runny nose, watery eyes, and sneezing, as well as anaphylaxis. Anaphylaxis is a severe allergic reaction that affects many parts of the body. Symptoms vary from mild to severe and may include breathing difficulties, shock, and loss of consciousness. Anaphylaxis is a potentially fatal reaction that requires immediate treatment.

General: Allergic reactions to vaccines are rare, and symptoms can range from mild to severe. The most serious allergic reaction, called anaphylaxis, can be life threatening. Symptoms can develop anywhere from several minutes to several hours after the vaccine is administered.

Anaphylaxis (anaphylactic shock): Anaphylaxis is a systemic allergic reaction, which means that many parts of the body are affected. Symptoms of anaphylaxis can vary from mild to severe and may include low blood pressure, breathing difficulties, chest pain, hives, and loss of consciousness. The time lapse between contact with the allergen and anaphylactic symptoms varies among individuals. Symptoms may appear immediately or may be delayed from 30 minutes to one hour after exposure. Symptoms may also disappear and then recur hours later. Once symptoms arise, they progress quickly. Anyone with symptoms of anaphylaxis should seek immediate treatment.

Angioedema: Some hypersensitive patients may experience angioedema in response to a vaccine. Angioedema refers to the swelling that occurs in the tissue just below the skin. Angioedema is similar to hives, except it occurs deeper in the skin. The swellings, known as welts, usually appear around the eyes and mouth. They may also be present on the hands, feet, and throat.

Asthma:Asthma symptoms, including coughing, wheezing, shortness of breath, or difficulty breathing, may be triggered by vaccine allergies, especially in infants and young children.

Hives: Some patients may develop hives. Hives are red, itchy swollen welts on the skin that may appear suddenly and disappear quickly. They often develop in clusters, with new clusters appearing as other areas clear up.

General: Patients who have suspected allergies may undergo allergy testing to confirm a diagnosis. If a patient tests positive to vaccine allergens (substances that trigger an allergic reaction), the vaccine may not be recommended, or it may be given in low doses over a longer period of time.

Patients who experience symptoms of anaphylaxis after receiving a vaccine are treated with epinephrine immediately. Because anaphylaxis is life threatening, a diagnosis is not needed to begin urgent medical treatment. Less-severe allergic reactions to vaccines can be diagnosed with either a skin test or allergen-specific immunoglobulin (IgE) test.

Skin test: A skin test is used to determine whether a patient is allergic to certain allergens that are contained in vaccines. During the test, the skin is exposed to different allergens. The skin is then observed for an allergic reaction. If an allergen triggers an allergic reaction to a test, the patient will develop reddening, swelling, or a raised, itchy red wheal (bump) that looks similar to a mosquito bite. The healthcare provider will measure the size of the wheal and record the results. The larger the wheal, the more severe the allergy. A skin test is typically conducted in a healthcare provider's office. Skin tests cause minimal, if any, discomfort. The needles used barely penetrate the skin's surface and will not cause bleeding.

Allergen-specific immunoglobulin (IgE) test: An allergen-specific immunoglobulin E (IgE) test, commonly referred to as radioallergosorbent test (RAST®), may also be used to determine whether the patient is allergic to certain allergens in vaccines. However, this test is less accurate than a skin test. It is usually performed in patients who have coexisting severe skin diseases (such as eczema or psoriasis) that make it difficult to interpret a skin test.

During the procedure, a sample of blood is taken from the patient and sent to a laboratory that performs specific IgE blood tests. The allergen is bound to a paper disc called an allergosorbent. Then the patient's blood is added. If the blood contains immunoglobulin antibodies (substances that detect and bind to foreign substances in the body) to the allergen, the blood will bind to the allergen on the disc. A radiolabelled ANTI-IgE antibody is then added to the disc to measure the level of immunoglobulin E present in the blood. The higher the radioactivity, the higher the level of IgE in the blood and the more severe the allergy.

A qualified healthcare provider will interpret the results of the test. In general, the sensitivity of these tests ranges from 50-90%, with the average being about 70-75%. The patient will receive test results in about 7-14 days.