What is injectable allergen immunotherapy?
Injectable allergen immunotherapy, also known as subcutaneous immunotherapy (SCIT), is a long-term medical treatment designed to reduce allergic disease at its source. Unlike standard allergy medications, which aim to relieve symptoms, SCIT seeks to modify how the immune system responds to allergens over time.
SCIT has been used internationally for more than a century and remains the most extensively studied and established form of allergen immunotherapy. In Australia, it is prescribed and supervised by clinicians with appropriate training in allergy and immunology and is most commonly used to treat environmental allergies such as dust mite and grass pollen allergy.
Rather than offering quick relief, SCIT is a structured, staged treatment that requires commitment. For appropriately selected patients, it may lead to sustained improvement in symptoms, reduced reliance on medications, and meaningful gains in quality of life.
How SCIT works: the immune science
Allergic disease occurs when the immune system overreacts to harmless substances such as pollens or dust mites. This overreaction is driven by allergy-specific IgE antibodies and the release of inflammatory chemicals that cause symptoms like sneezing, congestion, itching, and wheeze.
SCIT works by introducing very small, controlled amounts of the allergen through injections under the skin. Over time, the dose is gradually increased. This repeated, controlled exposure encourages the immune system to respond differently.
Key immune changes associated with SCIT include:
- A reduction in allergen-specific IgE activity
- An increase in protective IgG antibodies
- A shift toward regulatory immune cells that promote tolerance
- Reduced release of inflammatory mediators
Together, these changes help the immune system become less reactive when exposed to the allergen in daily life.
The SCIT treatment journey
1. Initial assessment and shared decision-making
Treatment begins with a comprehensive consultation. Your clinician will confirm your diagnosis, review previous treatments, assess suitability, and discuss alternatives. This is a shared decision-making process, and no treatment proceeds without informed consent.
2. Build-up phase
During the build-up phase, injections are given regularly (often weekly or fortnightly), with gradually increasing doses of allergen. This phase typically lasts several weeks to months, depending on the protocol used and individual tolerance.
3. Maintenance phase
Once the target dose is reached, injections are spaced further apart, commonly every 4–6 weeks. The maintenance phase usually continues for three to five years and represents the core of treatment.
4. Completion and follow-up
After completing the planned course, injections are stopped. Many patients continue to experience benefit for years afterward, although individual responses vary. Periodic follow-up helps assess long-term outcomes.
Effectiveness and expected benefits
SCIT does not cure allergy, and results cannot be guaranteed. However, extensive clinical experience shows that many appropriately selected patients experience:
- Reduced severity and frequency of allergy symptoms
- Reduced need for daily allergy medications
- Improved sleep, concentration, and daytime functioning
- Better asthma control in people with allergic asthma
Benefits typically develop gradually over months rather than weeks. For many patients, improvement continues to build over the first one to two years of treatment.
