Vaccine allergy


Patients receive vaccines to prevent infections and diseases from developing. Although rare, some patients may develop allergic reactions to vaccines. This may occur when an individual is allergic to one or more products contained in the vaccine. Most allergic reactions occur if the vaccine contains antibiotics, egg proteins, gelatin, or mercury.
Vaccines work by stimulating the body's immune system. Vaccines contain small amounts of disease-causing organisms that allow the immune system to produce antibodies to the foreign invader. Once antibodies are developed, the immune system is able to respond quickly to the infection if the disease-causing organism ever enters the body. Consequently, individuals become immune to the specific illness after receiving a vaccine.
Some vaccines require more than one shot to take affect. Some vaccines may contain live viruses or bacteria that have been weakened, while others may contain inactivated (killed) microorganisms.
Live, weakened vaccines, also called attenuated vaccines, contain disease-causing organisms. These organisms have been grown in a laboratory so that they are unable to actually infect the human patient. However, in rare instances, the vaccine may infect the recipient or those who come into close contact with a recently vaccinated individual. This is more likely to occur in individuals who have extremely weakened immune systems (such as chemotherapy or HIV/AIDS patients). In general, live vaccines, such as those for yellow fever and measles, mumps, and rubella (MMR), have shown to produce stronger immune responses than inactivated vaccines. Some patients may only need one shot to produce life-long immunity.
Other vaccines, such as the influenza (flu) and cholera vaccines, contain microorganisms that have been killed with chemicals or heat. In general, these vaccines induce an incomplete or short-lived immune response. Therefore, patients usually need to receive booster shots (additional doses of the vaccine to enhance its effectiveness). These vaccines are generally safer than live vaccines because there is no chance that they will infect the patient.
Some types of vaccines only contain disease-causing toxins that are produced by bacteria. These vaccines do not contain any microorganisms. For example, the tetanus vaccine contains a bacterial toxin produced by tetanus bacteria. This toxin has been altered so that it will not cause disease in humans. Patients who receive this type of vaccine will become immune to the specific disease-causing toxin.
Accellular and subunit vaccines are made with just part of the bacteria or virus. For instance, the Haemophilus influenzae type B and hepatitis vaccines are produced this way.
People may develop allergic reactions to any type of vaccine and/or its components. The severity and duration of allergic reactions to vaccines vary among patients. Symptoms can develop anywhere from several minutes to several hours after the vaccine is administered. Anaphylaxis, a systemic allergic reaction that can cause low blood pressure, breathing difficulties, shock, and loss of consciousness, may occur. Anaphylaxis is considered a life-threatening emergency that requires immediate medical treatment.
Epinephrine is a medication used to treat anaphylaxis. Other medications, including antihistamines and corticosteroids, may help treat other allergic symptoms associated with vaccines.

Related Terms

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allergy triggers in vaccines

Antibiotics: Polio vaccines contain streptomycin, polymyxin B, and neomycin. In addition, the measles, mumps, rubella (MMR), and chickenpox vaccine also contain trace amounts of neomycin. Thus, these vaccines may cause an allergic reaction in people who are allergic to these antibiotics.
Patients who are allergic to antibiotics should consult their healthcare providers before receiving antibiotic-containing vaccines. Depending on the severity of the patient's history of allergic reactions, a healthcare provider may not recommend these vaccines.
One of the most common drug allergies occurs in response to penicillin. However, there are currently no vaccines made with penicillin or penicillin-related antibiotics.
Eggs: The current measles, mumps, and rubella (MMR) vaccine contains trace amounts of egg proteins, to which some patients may be allergic. However, according to the National Advisory Committee on Immunization, MMR can be administered safely to 99% of patients with egg allergies.
The influenza vaccine, also called the flu shot, also contains egg proteins. Patients who are allergic to eggs should not receive this vaccine because it contains enough egg protein to trigger a severe, life-threatening reaction called anaphylaxis. The most severe symptoms of anaphylaxis include low blood pressure, breathing difficulties, shock, and loss of consciousness, all of which can be fatal.
The yellow fever vaccine is also made with egg proteins. Yellow fever, an often fatal viral infection, is a major concern for patients living in or traveling to South America or Africa. Therefore, patients who are allergic to eggs and are planning to visit these areas should discuss their options with their healthcare providers. Usually, patients who are allergic to eggs receive lower doses of the vaccine over a longer period of time. The doses are gradually increased until the patient is able to take the full dose. This process is called desensitization because the body builds up a tolerance to the egg proteins.
Gelatin: Some live vaccines, including MMR, chicken pox, and yellow fever, contain gelatin. This ingredient helps to stabilize the vaccine. Patients who are severely allergic to gelatin should consult their healthcare providers before receiving such vaccines.
Mercury (thimerosal): Thimerosal is a mercury-containing preservative that was once commonly used in vaccines. This ingredient helps kill any live contaminants in vaccines. However, in rare cases, thimerosal may trigger minor allergic reactions in sensitive patients.
Although no serious side effects have been reported from thimerosal at doses used in vaccines, the Public Health Service (PHS) agencies, the American Academy of Pediatrics (AAP), and vaccine manufacturers have agreed that the ingredient should be reduced or eliminated in vaccines as a precautionary measure. Currently, most vaccines in the United States do not contain thimerosal.