Allergy Shots and Sublingual Immunotherapy: Long-Term Treatment

For most people with pollen allergies, the right combination of avoidance, antihistamines, and nasal sprays is enough. But for those whose symptoms stay severe despite good treatment, or who react to multiple allergens, immunotherapy offers something different: it changes the immune system’s underlying response instead of only managing symptoms.

What immunotherapy is

Immunotherapy is the practice of giving gradually increasing doses of an allergen to retrain the immune system to tolerate it. Over time, the body produces different antibodies and modifies the cells that drive allergic reactions. The result is a real reduction in symptoms, often persisting for years after treatment ends. It is the only allergy treatment that addresses the cause rather than the symptoms.

There are two main forms:

Subcutaneous immunotherapy (SCIT): the traditional “allergy shots” given in a clinic.
Sublingual immunotherapy (SLIT): tablets or drops held under the tongue at home.

Both work. They differ in practicality, the range of allergens they cover, and the regulatory approvals in different countries.

Who it is for

Immunotherapy is usually considered when:

Symptoms remain severe despite correct use of standard medications
The person wants to reduce long-term medication use
Allergic asthma is triggered by allergens that are hard to avoid (see the pollen and asthma page for how that interaction usually looks)
The allergen is hard to avoid, such as grass pollen in a region with long, intense seasons

It is not a first-line treatment. It is a long commitment (typically three to five years), it carries some risk, and it is only suitable for confirmed allergies, usually established through skin-prick or blood tests.

How a course of treatment works

Subcutaneous immunotherapy (SCIT)

The standard course runs in two phases:

Build-up phase. Injections are given once or twice a week, with the dose increasing each time. This phase typically lasts three to six months.
Maintenance phase. Once the target dose is reached, injections are given once a month. This phase continues for three to five years.

After each injection, the patient waits in the clinic for 20 to 30 minutes because of the small risk of anaphylaxis. SCIT is highly effective for pollen, dust mites, and insect venom allergies, and effective for mould and pet dander where available.

Sublingual immunotherapy (SLIT)

SLIT comes as tablets or drops taken daily at home, usually starting a few months before the pollen season and continuing through it. The first dose is taken under medical supervision; subsequent doses are taken at home. Treatment typically runs three to five years.

Regulatory approvals vary. In the United States, SLIT tablets are approved for grass pollen, ragweed, and dust mites. In the European Union, a wider range of SLIT products is available, including drops that can be tailored to the individual.

Effectiveness

Immunotherapy is one of the most effective long-term treatments for allergic rhinitis. Trials and meta-analyses consistently find that it:

Reduces symptom scores by 30 to 50 percent on average
Reduces the need for symptomatic medications
Improves quality of life
Reduces the risk of new sensitisation and the development of asthma in children

Effectiveness is highest for single-allergen immunotherapy against the dominant trigger. People with multiple severe allergies may need to treat the dominant one first.

Risks

The most important risk is anaphylaxis, a severe, whole-body allergic reaction. It is rare (roughly 1 in 1,000 to 1 in 10,000 injections for SCIT, and rarer for SLIT) but it is the reason SCIT must be given in a clinic with emergency medication on hand. Local reactions (redness and swelling at the injection site, or itching and swelling in the mouth for SLIT) are common and usually mild.

Immunotherapy is not suitable for everyone. Severe asthma that is not well controlled, certain immune system conditions, and pregnancy are usual reasons to avoid or postpone treatment. A careful assessment by an allergist is essential before starting.

A note on individual variation

Some people notice a clear improvement within the first pollen season of treatment. For others, the difference becomes obvious only in the second or third year. The investment is real; the payoff, when it comes, is also real and durable.