Immunotherapy: How Allergy Shots Work

Benefits, Risks, and More

Vial for allergy shot
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When medications fail to adequately control allergy symptoms and avoidance of the trigger is not easy or possible, an allergist may recommend immunotherapy or “allergy shots.” This treatment consists of a series of injections containing small amounts of the substances to which a person is allergic.

After a course of allergy shots, 80 to 90 percent of patients have fewer allergy symptoms, and in many cases, their allergies have completely resolved.

Allergy shots can be given for allergic rhino-conjunctivitis (nose and eyes), allergic asthma, and insect sting allergies.

Overview

Allergy shots have been given for nearly 100 years and are FDA-approved therapies. Numerous well-designed medical studies show the efficacy of allergy shots. And allergy shots do not contain steroids, which can have adverse long-term side effects.

Unlike allergy medicines, which act only to “cover up” allergic symptoms or prevent them temporarily, allergy shots fix the underlying problem of allergies. This occurs because the body treats the injection much like a vaccine, resulting in the production of infection-fighting antibodies against the pollen, dust, mold or pet dander.

The body then stops producing as many allergic antibodies against the triggers and, therefore, won’t have as much, or any, allergic response when exposed to the allergens. These changes can last for many years, even after stopping allergy shots.

Recent studies show that allergy shots can also prevent people from developing new allergies and reduce the risk of developing asthma in children with nasal allergies.

Method and Dosage

The method of immunotherapy consists of starting at a small dose that will not cause an allergic reaction, with slowly advancing the dosage until the person becomes tolerant to large amounts of the extract.

These injections are initially given once to twice a week until a maintenance, or constant dose, is achieved. This usually takes approximately three to six months.

Once the maintenance dosage is reached, the allergic symptoms are largely resolved in most patients. Thereafter, the injections are given every two to four weeks.

Duration of Treatment

Therapy is continued for three to five years total, after which the patient continues to benefit for another five to 10 years or longer, even after the shots are stopped. If the shots are stopped prior to a total of three years, the allergic symptoms typically return more quickly.

Risks

The risks of immunotherapy consist of the possibility of experiencing an allergic reaction to the allergy shot. Most allergic reactions consist of mild to moderate swelling and itching at the site of the injection.

These reactions occur frequently, but rarely require any change in treatment. A large swelling may require an adjustment to the immunotherapy dosage or a change in the frequency and amount of the shots.

Less commonly, patients experience whole-body allergic reactions, sometimes called “anaphylaxis.” Most of these reactions are mild and consist of itching of the skin, hives, or a runny nose.

Others are more severe and can present as cough, chest tightness, wheezing, throat tightness, shock, and rarely can be life-threatening.

For this reason, it is normally required that patients remain in the physician’s office for 20 to 30 minutes after the injection since most reactions occur during this time. These reactions are typically easily reversed with medicines, such as injectable epinephrine and antihistamines.

Eligibility

Obviously, whether or not you are a candidate for immunotherapy is a question that only you and your doctor can answer. That said, there are many reasons to consider allergy shots:

  • Medications not working—Many patients go to the allergist because they still have symptoms despite having tried numerous allergy medications with little to no relief of their symptoms. Sometimes allergy shots are the only therapy left for these patients.
  • The concept of a "cure"—Other patients like the idea of a “cure” and opt for allergy shots for that reason. Remember, immunotherapy is the only treatment for allergies that fixes the underlying problem of the immune system, much like a vaccine.
  • Not liking to have to take medications—Some patients experience severe side effects from medications or don’t like taking medications on a daily basis. The idea of a once-a-month shot is a better option for them.
  • Medications are pricey—Medications can be expensive, and since allergy symptoms typically return soon after medications are stopped, patients may require medications for many, many years. Allergy shots can alleviate much of the need for medications and can be a significant cost savings measure in the long run.

Source:

American Academy of Allergy, Asthma and Immunology. Allergen Immunotherapy Practice Parameters. Ann Allergy Asthma Immunol. 2003; 90:S1-40.