The first immunotherapy treatments appeared in the early 1900's. This is a therapeutic option to consider in the treatment of respiratory allergies (pollens, dust mites, cats, mold) that are responsible for symptoms of asthma and/or rhinitis. Immunotherapy may also be useful in preventing the development of new environmental allergies, and in preventing the progression of rhinitis to asthma. This form of treatment is also recognized for allergies to venomous insects (several sorts of wasps, bees). Immunotherapy by injection is not a treatment at the present time for food allergies. Oral immunotherapy for food allergies is currently being investigated.
What is immunotherapy?
Immunotherapy consists of the administration either subcutaneously (by injection) or sublingually (oral) of a certain quantity of allergen known to cause the allergy. The amount administered gradually increases until a maintenance dose is reached. The maintenance dose is the maximal dose that the patient receives and it is this dose which will be the most effective.
By gradually and regularly exposing the immune system to a relevant allergen, we can observe different signs within the immune system that suggest a development of tolerance to this allergen, in addition to a reduction in the signs and symptoms of allergy caused by the allergen in question. In other words, our bodies slowly learn to tolerate this allergen. The method of exposure is important, because certain people believe that by being exposed directly to the allergen (example, a cat), that a similar tolerance develops; however, in this manner the immune system is exposed very rapidly to high concentration of allergen, and so will be unable to adapt gradually as is necessary.
Effectiveness of immunotherapy
Immunotherapy against insect venom is at the moment the most effective immunotherapy, with a level of efficacy approaching 98%.
About 80-85% of people receiving treatment with pollen immunotherapy see improvement in their condition. Immunotherapy is also recognized to be effective in the treatment of allergy to dust mites, molds, animal dander and cockroaches. This form of treatment does not guarantee complete resolution of allergic manifestations, but can have positive impacts on the quality of life in most patients.
Immunotherapy for allergic rhinitis may have benefits that persist even after stopping therapy at the appropriate interval. Despite this, it is always possible that in the long term allergic symptoms will return, and a second course of immunotherapy may be considered.
Who will benefit from a course of immunotherapy?
The following criteria are useful in determining who is a good candidate for immunotherapy:
- Adults and children with a proven allergy to venomous insects (see the section on Allergies to insect venom).
- The patient (adult or child) must have the clinical signs and symptoms of allergy. It is also essential that he or she has positive allergy tests (skin and/or blood tests) clearly demonstrating the presence of sensitization to certain allergens.
- Patients whose allergic symptoms are not well controlled, despite treatment with medication and environmental control measures.
- Patients who have side effects to medicines, and cannot take them.
- Patients who need to take several medicines to treat their symptoms and who wish to reduce, over the medium term, their use of medication.
- The patient must be able to commit to a treatment that is time consuming, and remain aware of the risks and benefits, realizing that improvement is not 100% guaranteed.
The following factors suggest that a course of immunotherapy is contraindicated:
- Negative allergy tests.
- Patients with positive allergy tests but no clinical signs or symptoms of allergy.
- Poorly controlled asthma is a contraindication for immunotherapy.
- Certain medications (certain medications for hypertension and cardiovascular disease in particular) can interfere with the treatment of an allergic reaction to immunotherapy. It is therefore important to mention all of your medications to your allergist - he or she may decide that immunotherapy may be still be given, or that your medications need to be replaced.
What kinds of therapy are available?
- Annual: the patient receives at least one injection per week for about 4-6 months. The dose gradually increases during this time until the maximum dose (maintenance dose) is achieved. This same dose will then be repeated monthly during a period of 3-5 years. This method is preferable when several allergies are involved.
- Pre-seasonal: a series of 4-11 injections that are administered before the pollen season in question. Only pollen allergies can be treated in this manner. This type of treatment is usually repeated during 3-5 years.
- Sublingual: this type of treatment consists of putting a quick dissolving tablet under the tongue. The first tablet is given under the supervision of the allergist with a period of observation of 30 minutes. The patient then takes one tablet daily at home for 6 months. The treatment normally starts 3-4 months before the allergic season, and continues during this season. One must repeat this treatment each year for at least 3 years. This form of treatment is now available in Canada for grass and ragweed pollen. Other allergens should be available in a sublingual form over the course of the next few years. This kind of treatment has an efficacity comparable to injections throughout the year. There is a much lesser risk of anaphylaxis. Principal side effects include itching of the mouth or throat, and swelling of the lips. These side effects mostly disappear after the first week of therapy.
What are the risks of immunotherapy?
- The biggest risk with this type of treatment is the development of an acute allergic reaction. Most of the time these reactions occur within 30 minutes of receiving the injection. It is still possible to have a reaction after 30 minutes.
- Reactions may involve the following:
- A local reaction: swelling, redness, warmth and itching at the site of injection. This type of reaction typically responds well to an antihistamine. Immunotherapy treatment can continue, although dosage adjustments may be necessary.
- Allergic symptoms of the eyes or nose (itching, tearing, redness, nasal secretions), swelling of the face (lips, eyes, nose).
- A systemic or generalized reaction (incidence < 0.6%): urticaria (redness and swelling of the skin), respiratory problems (shortness of breath, cough…), digestive problems (abdominal cramps, nausea, vomiting), hypotension, weakness. In these cases a doctor will need to treat you. You must also reassess your immunotherapy treatment with your allergist if you experience such a reaction.
- Exceptionally, deaths have been reported with immunotherapy (1 death for 2 million injections in the United States). Deaths have typically occurred in poorly controlled asthmatic patients during vaccine administration.
Recommendations when starting immunotherapy
- It is important to remain under observation in the doctor's office a minimum of 30 minutes after receiving an injection of immunotherapy, given the risks of a reaction.
- Before the injection, inform the doctor if you have had a worsening of your allergy symptoms, of your asthma, or other respiratory problems. Also, inform the doctor if you have started a new medicine (for example, medicine for high blood pressure) or if you are pregnant.
- Inform the doctor of any late reactions after the last injection. Don't rub or massage the injection site.
- Avoid intense physical activity within 2 hours following the injection.
- You should follow up with your allergist every 6-12 months.