Allergen Immunotherapy (AIT), commonly known as allergy shots, is a long-term medical treatment designed to reduce sensitivity to specific allergens. This therapy involves a multi-year commitment to lessen allergic symptoms and potentially modify the course of allergic disease. While AIT is widely regarded as an effective option for conditions like allergic rhinitis and allergic asthma, patients express concern about potential side effects. The most serious concern involves an adverse reaction that affects the respiratory system, potentially mimicking or worsening asthma symptoms. This article explores the mechanism behind AIT, addresses the risk of developing asthma-like reactions during treatment, and outlines the protocols in place to ensure patient safety.
How Allergy Shots Work
Allergy shots function by introducing carefully measured amounts of the specific substances that trigger a patient’s allergic reactions. This controlled exposure trains the immune system to tolerate the allergen over time. The therapy is divided into two distinct phases to achieve immune desensitization.
The initial stage is the buildup phase, where patients receive injections containing gradually increasing concentrations of the allergen extract. These shots are typically administered once or twice a week and last for approximately three to six months. The goal is to safely reach the maximum effective dose that the patient can tolerate.
Once this highest dose is achieved, the patient transitions into the maintenance phase, where the dosage remains constant. Injections are then given less frequently, usually every two to four weeks, and this phase continues for three to five years. This long duration of treatment is necessary to establish lasting changes in the body’s immune response.
The biological goal of AIT is to shift the immune response away from the typical allergic reaction pathway. Allergies are mediated by T helper 2 (Th2) cells, which promote the production of immunoglobulin E (IgE) antibodies. IgE is the antibody responsible for triggering the release of inflammatory chemicals like histamine when it encounters an allergen.
AIT promotes a different immune pathway, favoring T helper 1 (Th1) cells and regulatory T cells. This shift reduces the production of allergen-specific IgE and simultaneously stimulates the creation of “blocking antibodies,” primarily immunoglobulin G4 (IgG4). These IgG4 antibodies compete with IgE to bind the allergen, preventing it from attaching to mast cells and basophils, thereby suppressing the allergic response.
Identifying Asthma-Like Reactions
The question of whether allergy shots can cause asthma symptoms is directly related to the immune system’s response to the administered allergen. Since the injection contains the substance a person is allergic to, it carries a small but definable risk of causing a systemic allergic reaction. These systemic reactions can involve the lower respiratory tract, producing symptoms characteristic of an asthma exacerbation.
Specific asthma-like symptoms that can occur following an injection include wheezing, a whistling sound produced by constricted airways, and persistent coughing. Patients may also report chest tightness or shortness of breath, which are signs that the bronchial tubes have become narrowed. These symptoms represent a serious medical event, indicating a widespread allergic response, classified as a Type I hypersensitivity reaction.
It is important to distinguish these systemic reactions from common, less severe localized reactions. A localized reaction is confined to the injection site, typically appearing as redness, swelling, or itching on the arm. In contrast, a systemic reaction involves symptoms in a different body system, such as generalized hives, throat itching, or respiratory distress.
The presence of respiratory symptoms is a component of anaphylaxis, which is a rare but potentially life-threatening reaction. While systemic reactions are infrequent, estimated to occur in about 1 out of every 1,800 to 2,000 injections, respiratory symptoms are a notable part of this risk. Studies show that respiratory symptoms, either alone or combined with skin symptoms, account for a significant portion of all systemic reactions.
Managing Risk and Ensuring Safety
The primary factor influencing the risk of a systemic reaction is the patient’s existing respiratory health. Patients who have poorly controlled or unstable asthma are at a higher risk of experiencing a severe reaction to the injection. For this reason, physicians consider active or unstable asthma a contraindication, meaning the therapy should be deferred until the patient’s asthma is well-managed.
To mitigate the chance of a severe adverse event, rigorous clinical safety protocols are enforced across all allergy clinics. The most universal protocol is the mandatory 30-minute observation period immediately following the injection. The vast majority of serious systemic reactions, including those involving the airways, begin within this half-hour window.
The medical facility administering the shot must be properly equipped and staffed to manage an emergency. Injectable epinephrine, or adrenaline, must be immediately on hand, as it is the only medication that can counteract the effects of a severe systemic reaction like anaphylaxis. Patients are often advised to carry their own epinephrine auto-injector when leaving the clinic to address any rare delayed reactions.
Another safety measure involves dose management, which is adjusted for missed appointments or previous reactions. If a patient misses their scheduled injection by a certain number of days, the dose must be reduced to a safer level to prevent an excessive immune response. Similarly, if a patient experiences a significant local reaction, the dose may be lowered before the next injection to ensure continued safety. Patients are also routinely instructed to avoid strenuous physical activity for at least two hours after receiving a shot, as increased blood flow could speed up the absorption of the allergen and increase the risk of a reaction.