Asthma: Can specific immunotherapy reduce the symptoms, and how safe is it?

Specific immunotherapy (“desensitisation”) can reduce the number of asthma attacks in people with allergic asthma. When injected, mild reactions in the tissue around the injection site are common. There is a small chance of a dangerous reaction to the injection that would need immediate medical treatment.

Bronchial asthma is a chronic disease in which the airways, especially the bronchi, are constantly inflamed. The bronchi over-react to particular things like physical exercise, cold air or substances that trigger allergies. This can lead to an asthma attack: people’s airways become narrower, they have breathing problems and make a wheezing sound when they breathe out. Asthma attacks often also cause coughing and a tight chest.

In a lot of people, asthma is closely linked to an allergy. Their asthma attacks are mainly triggered by allergy-causing substances such as pollen, dust mites or animal hair. Specific immunotherapy (SIT) may be considered as a treatment option for this kind of asthma. The aim of the treatment is to prevent asthma attacks by making the body less sensitive to the substances causing them. This treatment is also called desensitisation or hyposensitisation.  

In specific immunotherapy, people are exposed to small amounts of the substances that they have an allergic reaction to in order to make them less sensitive to those substances, or “desensitise” them. This can only be done if extracts of the allergen – the substance which triggers the allergy – are available for the treatment. This is currently possible for things like animal hair, dust mites, pollen and mold.

In immunotherapy, the allergen extract can either be injected into the skin (subcutaneously) or placed under the tongue (sublingually) in the form of drops, tablets or a spray. The treatment usually takes two to three years in total.

Research on specific immunotherapy in asthma

Researchers from the Cochrane Collaboration – an international network of researchers – wanted to find out what people with asthma can expect from specific immunotherapy. They did a systematic review. In other words, they combined and analysed the results of all the reliable trials of immunotherapy in asthma. This is important because it is only possible to get a realistic picture of the advantages and disadvantages of a treatment if you consider all of the research in that area together. You can read more about how systematic reviews are done here (URL: http://www.informedhealthonline.org/here.61.en.html) .

The researchers found 88 trials of immunotherapy in asthma, involving just under 3,500 people. They only included trials of subcutaneous immunotherapy, where the solution was injected into the skin. Both adults and children took part in the trials.

Specific immunotherapy can prevent asthma attacks in some people

The research showed that specific immunotherapy really can help people who have asthma: symptoms got worse in 6 out of 10 people who did not have immunotherapy (60%), compared to only 3 out of 10 people who had the “allergy shots” (30%). In other words, specific immunotherapy prevented some asthma attacks in 3 out of 10 people (30%).

The treatment also had another effect: people who had specific immunotherapy needed less medication for their asthma symptoms overall. About 2 out of 10 people who had immunotherapy needed to use less medication (20%).

Although some trials have shown that the effects of specific immunotherapy in asthma last for several years, it is not known how long these effects actually last.

Mild skin reactions at injection site are common

If the allergen is injected into the skin, it is quite common for people to have a temporary local skin reaction at the injection site – usually swelling or a rash. In up to 2 out of 10 people, the injections led to stronger allergic reactions or asthma symptoms which sometimes needed medical treatment (up to 20%).  

In very rare cases immunotherapy injections can lead to anaphylactic shock. This is a life-threatening allergic reaction in the body. It is a medical emergency and must be treated immediately. Because of this, people who have an injection have to be monitored by a doctor for at least 30 minutes following the injection so that the doctor can give immediate treatment if necessary. Your doctor will tell you about the signs of anaphylactic shock so that you know what to look out for.

The risk of anaphylactic shock is normally very small. However, it is considerably higher if you have very severe asthma and your symptoms cannot be kept under control with medication. If that is the case, specific immunotherapy may not be considered as a treatment for you. People who have heart problems or take beta-blockers also have a higher risk of anaphylactic shock.

You can read more about specific immunotherapy in our fact sheet (URL: http://www.informedhealthonline.org/fact-sheet.375.en.html) , which also has information about sublingual immunotherapy (SLIT), where drops or tablets are placed under the tongue.

Author: German Institute for Quality and Efficiency in Health Care (IQWiG)