Immunizations are methods of vaccinating patients against certain diseases. In most cases, patients do not experience an adverse reaction to these vaccines. However, in rare cases vaccines may trigger allergic reactions, including life-threatening anaphylactic shock.

Children make up the majority of immunization patients. Many parents feel torn between a desire to protect their children against ailments such as influenza, measles or pneumonia, and a fear of exposing a child to potential health risks triggered by a vaccine.

However, recent research indicates that allergic reactions to immunization therapy are rare. Patients most likely to react are those with food or medication allergies, but even among those populations there is very little likelihood of suffering severe reactions.

Not all reactions to vaccines are allergic reactions. People may experience side effects that are not immunoglobulin E (IgE)-mediated. These reactions may be limited to a certain body part (localized) or appear throughout the body (generalized). Such reactions include tenderness at the injection site (local) or fever (general). These side effects are considered minor and do not prohibit further use of the vaccine.

Experts generally agree that for most patients, the potential benefits of vaccination far outweigh the small risks involved. For example, the U.S. Centers for Disease Control and Prevention (CDC) reports that children who are not vaccinated against measles are 35 times more likely to contract the disease than those who receive immunization.

Immunizations are preventative treatments that keep people from contracting various diseases. These vaccines can inoculate patients against measles, mumps and rubella; diphtheria, tetanus and pertussis; influenza and many other health risks. However, these same vaccines can trigger symptoms in some patients who have allergies.

Not all reactions to vaccines are allergic in nature. Many patients will experience side effects to immunization procedures that are not IgE-mediated. These reactions can be localized (limited to part of the body) or generalized (systemic, and appearing throughout the body). Symptoms include:

• Localized
• Pain
• Warmth
• Tenderness
• Swelling
• Erythema (skin redness caused by dilatation and congestion of the capillaries)
  
  
• Generalized
• Fever

Such side effects usually are considered minor and do not prohibit further use of the vaccine. In addition, some physical causes related to the actual act of injecting can mimic an allergic reaction.

In some cases, vaccine-related reactions manifest as a skin irritation such as a rash (contact dermatitis) or hives. In other cases, symptoms can be more severe, such as the potentially life-threatening reaction called anaphylactic shock.

Signs and symptoms of a severe allergic reaction may include:

• Difficulty breathing (e.g., wheezing)
• Hoarseness
• Weakness
• Dizziness
• Swelling of the mouth and throat.
• Paleness
• Rapid heart beat

Allergic reactions to a vaccine typically occur within several minutes to several hours after the vaccine is given. Parents of children displaying the signs of symptoms of a severe allergic reaction should seek immediate emergency medical attention for the child. Parents with children showing other unusual symptoms (e.g., high fever, behavior changes) after receiving a vaccine should contact their physician.  

Children make up the majority of immunization patients. Parents may feel torn between a desire to protect their child from disease, and a fear that doing so could trigger potentially life-threatening allergies.

However, recent research indicates that allergic reactions to immunization therapy are rare.  Only about one in a million doses of a vaccine triggers a severe allergic reaction, according to the U.S. Centers for Disease Control and Prevention (CDC). Patients most likely to react are those with food or medication allergies, but even among those populations there is very little likelihood of suffering severe reactions.

Vaccines are safe. Each vaccine must undergo rigorous testing to ensure safety before the U.S. Food and Drug Administration (FDA) approves it for use. This process can take a decade or longer. In addition, the FDA and the CDC monitor all approved vaccines through a program known as the Vaccine Adverse Event Reporting System.

Failure to vaccinate a child against certain diseases dramatically raises the chances of health risks for the child. Children are more likely to contract common, contagious, preventable and potentially deadly diseases. This raises the potential for the re-emergence of diseases in areas where they were once almost eradicated.

Experts agree that for most patients, the benefits of vaccination far outweigh the small risks involved.

Most people who receive vaccines will experience no allergic reaction to the medication. Allergic reactions are rare for virtually all vaccines. However, certain ingredients commonly found in vaccines may trigger symptoms in those who have allergies to the specific ingredient.

Gelatin is frequently a source of allergic reactions to vaccines. It is used as a stabilizer in vaccines. Those with gelatin allergy have the potential to react when being immunized with any of the following vaccines that contain gelatin:

• Diphtheria, tetanus and pertussis (DTaP)
• Influenza
• Japanese encephalitis
• Measles, mumps and rubella (MMR)
• Rabies
• Varicella
• Yellow fever

Gelatin is not the only allergic trigger associated with vaccines. Egg protein is also a common source of allergic reaction to vaccines. While allergens are often contained within the vaccine, individuals with latex allergies may react to vaccines supplied in rubber-containing vials or syringes.

Vaccines that have caused allergic reactions in some people include:

• Hepatitis A (infectious hepatitis). This vaccine rarely causes reactions in patients, but mild to severe allergy symptoms may occur.
  
  
• Hepatitis B (serum hepatitis). Some patients have experienced anaphylactic episodes when receiving this vaccine. Some experts warn that those with an allergy to baker’s yeast should not get this immunization, as the vaccine contains baker’s yeast. However, other studies say there has never been a substantiated claim of a vaccine-related reaction to this yeast.
  
  
• Measles, mumps and rubella (MMR) vaccine. A very small percentage of children may have an anaphylactic response, which is likely a reaction to the gelatin used as a stabilizer in the vaccine. However, most experts say this tiny risk pales in comparison to the potential benefits from the vaccine. Each of the three diseases can cause serious consequences, including death (measles), brain infection (measles and mumps), and birth defects and mental retardation (rubella).
  
  For years, it was believed that children with egg allergies were highly susceptible to reacting to MMR vaccine. In preparing measles vaccine, the virus must be incubated in cell cultures that contain chicken cells derived from the egg. However, recent studies have found no connection between egg allergy and reaction to the MMR vaccine. Parents are urged to consult with a physician about the source of the vaccine and whether or not to vaccinate children who are allergic to eggs. Some physicians may choose to perform a skin test on the child prior to administering the vaccine.
  
  
• Diphtheria, tetanus and pertussis (DTaP) vaccine. Generalized reactions to the vaccine are rare; however some patients develop IgE antibodies to this vaccine but usually receive subsequent doses without an allergic reaction.
  
  
• Smallpox vaccine. Those with atopic dermatitis or with a history of the condition should not be vaccinated for smallpox, according to U.S. Centers for Disease Control (CDC) guidelines. The only exception to this rule would be during an outbreak of smallpox. In such cases, the potential protective benefit may be worth the risk of side effects. The most vulnerable patients include:
  
  
• • Patients with atopic dermatitis, or a history of the condition.
    
    
  • Patients with congenital or acquired immune deficiency diseases such as AIDS.
    
    
  • Patients taking immunosuppressive drugs. These drugs are often taken by those receiving organ transplantation.
    
    
• Influenza vaccine. Severe allergic reactions to this vaccine are rare. Those with egg allergies or a previous reaction to this vaccine should not be immunized with a yearly flu shot. This vaccine is grown in chicken eggs. Although almost all of the egg protein is filtered out of the final product, some of the allergen may remain. One study done in the late 1980s found that up to one-third of those who receive influenza vaccine showed an increase in IgE antibodies to egg protein when tested.
  
  
• Haemophilus influenzae Type B vaccine.  Also known as Hib disease, Haemophilus influenzae Type B is a bacterial illness that can cause a potentially fatal brain infection in young children. Reports of reactions to this vaccine have been rare.
  
  
• Pneumococcal vaccine. This vaccine can help prevent the lung infection pneumonia, which is caused by pneumococcus bacterium. Allergic reactions are rare, but can occur in some patients.
  
  
• Meningococcal vaccine. Protects against meningococcal disease, a bacterial infection that can lead to bacterial meningitis. This potentially life-threatening disease involves an inflammation of the membrane that covers the brain and spinal cord. Serious allergic reactions to this vaccine are rare.
  
  
• Yellow fever vaccine. People with egg allergies have experienced anaphylactic reactions, as the vaccine is cultured in chicken embryos and contains egg protein.
  
  
• Japanese encephalitis vaccine. Some patients experience hives and wheezing from five minutes to an hour after receiving the vaccine. In addition, this vaccine sometimes can trigger a late-onset combination of hives and angioedema. This often takes place two to three days after immunization. Symptoms usually are confined to the skin, but sometimes blood pressure drops (hypotension) and the individual experiences respiratory stress. Some studies have suggested a link between prior history of hives, asthma, rhinitis or eczema and this late-onset condition.
  
  
• Varicella vaccine. This chickenpox vaccine can cause symptoms consistent with anaphylaxis. It is believed that gelatin used as a stabilizer in the vaccine is the likely cause of reactions.

In evaluating a potential allergic reaction to a vaccine, a physician will take a medical history and perform a physical examination. The physician may also take the following steps:

• Determine if the nature and timing of reactions are consistent with anaphylaxis.
  
  
• Obtain a history of similar reactions to the vaccine, or to other similar vaccines.
  
  
• Obtain a history of allergic reactions to foods.
  
  
• Determine if the patient will need additional doses of the vaccine or a substitute in the future. If not, the patient may simply be diagnosed as allergic to the vaccine, and no further treatment will be required. However, the patient may be more extensively tested to ensure an accurate diagnosis and to prevent exposure to other vaccines or foods that may cross-react with the allergen.

A physician may also perform allergy skin tests to confirm an allergy to a vaccine. Such testing must be done under close supervision and in a medical facility, as there is a small chance that the test itself could induce anaphylactic shock.

Treatment of an allergy related to immunization will depend on the symptoms that appear. Contact dermatitis reactions of the skin are likely to be treated with corticosteroids or another medication used to treat skin-related allergies. A drug called epinephrine would be used in cases of anaphylactic shock.

Avoidance is the best method for preventing reactions to immunization medicines. Children who experience a reaction to a previous dose of a vaccine should not receive another dose. Those with a known severe allergy to a vaccine component (e.g., gelatin) should not receive a dose of any vaccine containing that substance. In some cases, alternative vaccines can be used that do not cause a reaction. If no alternative is available, the symptom-producing vaccine may be given at lower doses.

An allergy skin test is commonly performed before lower doses of the vaccine are administered. If the results are positive, and the vaccine is necessary, the vaccine will be given in small, incremental doses.  Since even a tiny dose may trigger a life-threatening reaction, the vaccine should only be given in a facility that is equipped to handle anaphylaxis.

Preparing questions in advance can help parents to have more meaningful discussions with their child’s physicians. Parents may wish to ask their child’s doctor the following questions related to immunizations and allergies:

1. Do my child’s allergies put him or her at risk for severe reactions to vaccines?
   
   
2. How will I know if my child is having an allergic reaction to a vaccine?
   
   
3. If my child is allergic to the vaccine will the reaction be immediate?
   
   
4. What symptoms would warrant me calling for emergency help?
   
   
5. Is my child likely to be allergic to other vaccines as well?
   
   
6. Is there an alternative available for the vaccine my child is allergic to?
   
   
7. If one of my children is allergic to a vaccine, should I prevent my other children from getting it?
   
   
8. Does my child’s reaction to immunizations indicate a future food allergy?