Allergen Immunotherapy (AIT), commonly referred to as allergy shots, is a long-term treatment designed to reduce or prevent allergic symptoms by changing the body’s reaction to specific triggers. This approach involves injecting small, increasing amounts of the substance a person is allergic to, such as pollen or dust mites, beneath the skin. The goal is to gradually desensitize the immune system, leading to a state of learned tolerance. Understanding the duration of treatment involves two separate concepts: the short physical presence of the injected substance and the much longer duration of the immune system’s modified response.
The Immediate Presence of the Injected Allergen
The physical substance contained within an allergy shot, the allergen extract, does not remain in the body for an extended period. Once the dose is administered subcutaneously, it is absorbed into the bloodstream relatively quickly and metabolized by the body. The extract is short-lived, typically being absorbed and cleared within hours to a few days. This rapid clearance is why patients in the initial, or “build-up,” phase require injections as frequently as one to three times per week, ensuring the immune system receives consistent exposure for desensitization. Some extracts are mixed with an adjuvant, such as aluminum salts, which helps slow the release from the injection site, but the most common side effects, like localized swelling, usually resolve within 24 to 48 hours.
The Duration of Immunological Tolerance
The long-term benefit of allergy shots relies on fundamental changes induced in the immune system, not the physical presence of the dose. The treatment works by reprogramming the body’s response, shifting it away from an allergic reaction driven by IgE antibodies. This shift involves creating regulatory T-cells and promoting a protective response involving IgG antibodies, specifically IgG4. This process establishes immunological tolerance, which acts as an immune system “memory.”
This learned tolerance provides the lasting therapeutic effect, even after injections are stopped. Studies show that after successfully completing the full course of treatment, clinical benefits can persist for several years. While a common range for sustained relief is two to three years, many patients report continued improvement for five to 10 years or longer. This long-term effect is considered disease-modifying, meaning it alters the underlying allergic disease rather than just masking symptoms like medication.
Factors Influencing Long-Term Efficacy
The duration of benefit for any single patient is influenced by several variables related to the patient and the treatment. The length of time spent in the maintenance phase is a primary determinant of long-term success. Guidelines typically recommend a minimum of three to five years of maintenance injections for the best chance of sustained tolerance.
Patients who discontinue treatment prematurely, such as after only one or two years, risk their allergic symptoms returning sooner. Adherence to the recommended schedule is also important, as inconsistent dosing can hinder the immune system’s ability to solidify tolerance. Poor adherence, particularly during the first year, is a common reason for a lack of lasting benefit.
The specific allergen being treated can also play a role in the long-term outcome. Studies have noted differing relapse rates between those treated for pollen allergies versus dust mite allergies. Individual biological variations, such as the severity of the initial allergy and the patient’s unique response rate, mean that the duration of tolerance will ultimately vary.