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.