Administration of allergy shots, more appropriately called “specific allergen immunotherapy” or “allergen vaccine therapy,” is one of the oldest forms of treatment for allergic rhinitis and conjunctivitis. At the turn of the 20th century, it was discovered that injection of increasing doses of grass allergen into patients with summer hay fever resulted in a marked improvement in seasonal nasal and eye symptoms. It is now recognized that injections of allergenic extracts, including grass, tree, and weed pollens, house dust mites, cat and dog danders, cockroaches, and molds, substantially reduce symptoms of seasonal or perennial rhinitis in up to 80% of patients.
Allergy immunotherapy is usually considered in patients who (1) do not respond adequately to a trial of medications; (2) have significant side effects with medications; (3) begin to develop the involvement of other parts of the respiratory tract in their allergic disease, such as asthma, sinusitis, or middle ear disease; and (4) require a large number of medications that are costly to the patient. Immunotherapy is given once to twice weekly while the dose of allergen is being increased over a period of 4 to 6 months (“buildup phase”). Once the patient has achieved the top dose of allergen extract, the dosing interval is increased to 4 weeks, which is continued for approximately 3 to 4 years (“maintenance phase”), depending upon the response of the patient. Clinical benefits may be seen as soon as 3 months after starting injections but may not become apparent until the patient has been on a full maintenance dose for at least 3 months (usually 9 to 12 months of immunotherapy).
Most longterm studies show that the average level of improvement is 50% compared with the baseline level and that this benefit will last at least 2 to 3 years after stopping the therapy. Many patients will have very longlasting changes in their allergy symptoms, while some will need to restart their shots within 1 year of discontinuing immunotherapy. The most common adverse effects of allergy vaccine therapy is a large local area of redness, warmth, and itching of the skin at the injection site, which occurs within minutes to hours after the shot. This reaction occurs in at least 10% of patients at some time in their allergy shot program and rarely prevents a patient from reaching the full maintenance dose of allergenic extract. Immediate treatment of the reaction includes the use of ice and oral antihistamines. If these local reactions become recurrent and troublesome, administration of an oral H1 antihistamine, such as cetirizine (10 mg) or loratadine (10 mg), 2 hours before the shot may be helpful. If this alone does not work, the doctor can add the H2 antihistamine ranitidine (150 mg) or the leukotriene blocker montelukast (10 mg) , which may provide an additional benefit.
Much more worrisome than these large local skin reactions is the possibility of systemic reactions. These reactions usually occur within 20 to 30 minutes after the injection, and mild systemic reactions may include hives, flushing and itching of the skin, and discharge from the nose. More severe episodes usually involve wheezing, throat swelling, and/or a drop in blood pressure. These more severe reactions are referred to as anaphylaxis, and episodes accompanied by significant drops in blood pressure (<90/60 mm Hg) are referred to as anaphylactic shock. Surveys of large allergy shot populations have shown that approximately 1 in every 200 injections will result in some type of systemic reaction; thus most patients receiving allergy shots will never experience a reaction of this type. Contraindications for starting allergy shots include pregnancy, ischemic heart disease, poorly controlled asthma, and active autoimmune disease, such as systemic lupus erythematosus.
Sarah’s comment:
Starting about 5 or 6 years ago, my allergies were so bad that I missed at least a week of school every fall and occasionally in the spring. First, I would have a few days of sneezing and a stuffy, drippy nose, and then the wheezing would kick in, which kept me up half the night two or three nights per week. I used all kinds of antihistamines, nasal sprays, and an inhaler called Advair, which did seem to help a lot.
I also used my Proventil inhaler some days up to 5 or 6 times, and I would always end up on a Medrol Dosepak at some point in the fall. My doctor referred me to an allergist, who allergy tested me and found that I was very allergic to birch tree, ragweed, sage weed, and a mold called Alternaria. He strongly suggested that I take a course of allergy shots, which I have been doing for the past 3 years. After about a year of weekly injections, I began to feel much better, and last spring and fall I only had mild allergies without any major wheezing. I still use my Proventil inhaler but only need it every few days. The shots made a major difference in my life.