Immunotherapy — also known as "desensitization" or "allergy shots" — can gradually shift the way your body reacts to the substance causing your allergy so that you no longer experience allergy symptoms. Although most people who keep up with the shots will see improvement, the improvement does not usually occur until several months after the injections begin, and it may not be obvious until a year into treatment. Immunotherapy is usually reserved for people who aren't helped by drugs or require an expensive combination of drugs, who have allergy symptoms during most months each year, and who can't avoid the triggers (called allergens) that cause their symptoms. The shots are able to treat allergies to insect stings, pollens, molds, dust mites, cockroaches, or animal danders such as dog or cat.
Allergy shots aren't practical for food allergies, because injections with food allergens too frequently cause a severe allergy reaction (anaphylaxis). Scientists are trying to develop a safe injection that might be useful for neutralizing peanut allergy by developing a man-made protein that mimics the peanut protein but does not cause anaphylaxis. This treatment has been tested on mice, but it is not yet available for treatment of people. Another area of research for food allergy is the idea of desensitization by repeated miniscule oral doses of peanut. This treatment plan—called oral immunotherapy—has not yet been determined to be completely safe but it is promising. It uses the same scientific idea as do allergy shots.
Immunotherapy requires a major time commitment and a great deal of patience. Treatment begins with injections of small, diluted doses of the allergen. At first, you will have shots once or twice a week; after a few months, the schedule is cut back to every other week, then every three weeks, and then once a month. With every shot, you get a slightly higher dose until you reach the maximum dose, or a "maintenance" level, that you can tolerate without developing an allergic reaction.
If you do not have a clear improvement in your symptoms after getting shots for a year, you are unlikely to benefit by continuing. Typically, if you have improved in the first year, you will be advised to continue your allergy shots for at least three years. After that length of treatment, about one out of three people will maintain their improvement in allergy symptoms during future years, even though the shots have been stopped. Two out of three people will have symptoms return within the next year. Some people choose to continue allergy shots indefinitely, because they prefer not to take a risk that their allergies might recur.
In some cases, immunotherapy can be "rushed" so that you get the first phase of injections every few hours instead of every few days. This is sometimes done when people with a severe penicillin allergy need to have a serious infection treated with a penicillin-like drug. However, because of a greater danger of a reaction, "rush" immunotherapy must be done in a hospital setting by an experienced medical team.
How Does Immunotherapy Work?
If you have not had immunotherapy, your allergic reactions begin when your immune system releases a burst of antibodies. These antibodies are called IgE antibodies. IgE antibodies cause specific cells in your body to shower their surroundings with “histamine,” a protein that results in allergy symptoms.
When you are very regularly exposed to small, manageable quantities of an allergen, as you are when you receive allergy shots, your immune system shifts its strategy. Instead of responding in a burst of IgE antibodies, your body methodically produces a steady quantity of a different antibody type, IgG antibodies. Your immune system also activates immune cells called “suppressor T cells” that can reliably eliminate the protein from your system. When the IgG and T-cell system is in full swing, your body does not seem to feel the need to react to an allergy exposure with a full burst its more bothersome IgE antibodies. Also, in the presence of the IgG antibodies, an IgE antibody is less likely to trigger histamine release.
Are You A Candidate?
You are a particularly good candidate for allergy shots if you already require several expensive medications to keep your symptoms under control (for example, if you require a nose spray for hay fever as well as an inhaler for asthma). If you have allergy symptoms in many months of each year, and if you are allergic to substances which are hard to avoid, like trees and grasses, allergy shots may be practical. Immunotherapy is strongly recommended for people with severe allergic reactions to insect stings.
You will only be a good candidate for allergy shots if you are confident that you can keep up with the injections on a regular schedule. You need to have access to reliable transportation, and you need to have the flexibility in your work and travel schedule to permit office visits on a regular schedule that will continue for several years.
Although generally safe, immunotherapy is not without side effects. It is common for people to have a small amount of swelling and itching at the site of the injection. Such local reactions are common and last several hours or days. (This common reaction doesn't mean you have to discontinue treatment, but you may need an antihistamine to control the symptoms.)
There's also a risk of a more severe and life threatening reaction to the injected allergen. These reactions occur in just over 1 out of every 150 allergy shot injections. In some of these cases, the severe allergy reaction known as anaphylaxis can occur. Anaphylaxis can cause a person to develop a blocked airway, asthma, or low blood pressure, so it can be life threatening if it does not receive immediate treatment. Because of this danger, allergy shots should be given only when a doctor is present and in a facility equipped to handle life threatening emergencies. You must remain for observation 20 to 30 minutes after each injection so that you can receive immediate treatment if you have a severe reaction.
Severe asthma attacks can also develop as a reaction to the shots. Your doctor should have the appropriate staffing and facilities to handle an emergency should one occur. Because of the risks, asthma patients receiving allergy shots should check their peak flows before each injection. If not within 80 percent of best, the injection should be postponed.