Immunotherapy

Immunotherapy (commonly referred to as "allergy shots") is a highly effective treatment for patients with allergies. It is based on the premise that people who receive injections of a specific allergen will lose sensitivity to it. The most common allergens for which shots are given are house dust, cat dander, grass pollen, and mold.

Immunotherapy benefits include:

  • Targeting the specific allergen.
  • Reducing sensitivity in airways in the lungs as well as in the upper airways.
  • Preventing the development of new allergies in children.
  • Reducing asthma symptoms and the use of asthma medications in patients with known allergies. Research suggests it may also help prevent the development of asthma in children with allergies.

Candidates

Candidates for Immunotherapy. Immunotherapy may be given to anyone over age 7 whose allergies are severe and who do not respond to medication. Many experts agree that immunotherapy should be considered as soon as possible for children with asthma and allergies. Immunotherapy is safe for pregnant women who are already receiving it, although half-strength doses are generally recommended, and it should not be started during pregnancy.

Individuals at Risk for Complications. People who should probably avoid immunotherapy include those who have:

  • An extreme response to skin tests (this may predict an allergic reaction).
  • Wheezing.
  • Uncontrolled severe asthma or lung disease.
  • Patients taking certain medications (such as beta-blockers).
  • The health status of anyone should be determined before starting treatment.

Administering Therapy

The major downside to immunotherapy is that it requires a prolonged course of weekly injections. The process generally includes:

  • Injections of diluted extracts of the allergen are given on a regular schedule, usually twice a week to weekly at first, then in increasing doses until a maintenance dose has been reached. It usually takes several months and may take up to 3 years to reach a maintenance dose.
  • At that time, intervals between shots can be 2 to 4 weeks, and the treatment is continued for another 3 to 5 years.
  • Patients can experience some relief within 3 to 6 months. If there is no benefit within 12 to 18 months, discontinue the shots.

After stopping immunotherapy, about a third of allergy sufferers no longer have any symptoms, a third have improved symptoms, and a third relapse.

The use of an injection series is effective, but patients often fail to comply with the regimens. Some other schedules and delivery methods are being investigated that might make the program easier and less distressing.

Rush Immunotherapy. Investigators are studying "rush immunotherapy," in which patients achieve the full maintenance dose with several shots a day over a period of 3 to 5 days. Rush therapy uses modifications that reduce the risk of severe reactions to excessive doses. Studies suggest that it is effective and safe, with few side effects other than itching. Patients must be monitored closely during this period, however, for severe reactions.

Oral Forms. Trials are underway to test oral forms of immunotherapy as an alternative to allergy shots. These methods include using a pill taken by mouth or a sublingual (under-the-tongue) tablet. Although oral and sublingual immunotherapy is prescribed in many countries in Europe and South America, it is not approved in the United States and is not considered accepted therapy at this time.

Side Effects and Complications of Immunotherapy

Injections for ragweed and, sometimes, dust mites have higher risks for side effects than other allergy shots. If complications or allergic reactions develop, they usually occur within 20 minutes, although some can develop up to 2 hours after the shot is given.

Side effects of immunotherapy include:

  • General itching, swelling, red eyes, hives, soreness at the injection site.
  • Less common side effects are low blood pressure, asthma worsening, or difficulty breathing. This is due to an extreme hypersensitivity response called anaphylaxis. It can also occur if excessive doses are given.
  • In rare cases, particularly because of excessive doses or if a patient has a serious lung problem, severe reactions can occur, which can be life threatening.
  • Premedicating patients with antihistamines and corticosteroids may help reduce the risk of reactions to immunotherapy, although this could mask early warning signs.

In a 10-year study, the incidence of any adverse effect was less than two-tenths of 1 percent, and the great majority of events were mild. The risk for a fatal response is estimated to be 1 per 63 million injections. (As a comparison, the risk for a fatal reaction to penicillin is much higher, 1 per 7.5 million injections.)

Investigative Immunotherapy Approaches

Vaccines. Of particular interest is the development of immunotherapeutic vaccines that use more specific targets to produce an insensitivity to allergens. One such vaccine uses a small protein from the allergen, which is injected into the patient. Other vaccines under investigation are those that use the allergen's genetic material (its DNA) to promote tolerance to the allergen.

Monoclonal Antibodies. Monoclonal antibodies (MAb) are genetically-developed antibodies that are designed to target and attack very specific factors. A MAb known as omalizumab (Xolair) prevents the antibody immunoglobulin E (IgE) from triggering the inflammatory events that lead to allergies. Studies in recent years suggest that omalizumab is very effective in reducing symptoms and improving quality of life for patients with non-seasonal allergic rhinitis. A 2006 study suggested that treatment with omalizumab before and during ragweed allergy shots may help reduce immunotherapy side effects. The drug is currently approved for asthma.

Review Date: 3/17/2006
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.