Desensitisation (also known as immunotherapy) is the practice of administering gradually increasing doses of an allergen extract (eg pollen) in order to reduce the symptoms of the hayfever or asthma that it causes. It was first carried out almost 100 years ago to pollens and is now in widespread use around the world as a safe and effective treatment for allergies caused by different pollens, house dust mites, cat, dog and horse. It is sometimes referred to as ‘allergy vaccination’.
What are the benefits of allergen immunotherapy?
Large scientific studies have confirmed that immunotherapy can be used to reduce the symptoms of allergic rhinoconjunctivitis (hayfever) and seasonal asthma caused by grass or tree pollen as well as dust mite. Most patients receiving treatment also report needing to use less medication. As immunotherapy actually changes the way the body’s immune system reacts to the allergen, the beneficial effects continue beyond the 3 years that the treatment is given for.
Immunotherapy against year round allergens such as cat, horse or dog are also available although less is known about how well these treatments work although they do seem to be effective. Using immunotherapy from an early age may actually prevent new allergies developing and reduce the likelihood of getting asthma in later life. However, immunotherapy only works against a particular allergen. So, for example, having immunotherapy to grass pollen may help with hayfever symptoms during the summer (which are caused by grass pollen) but will not improve symptoms caused by other allergens such as house dust mite, during other times of the year.
There are different ways of performing desensitisation. These include:
- Subcutaneous Immunotherapy: this involves giving a series of injections to desensitise the patient. We currently do this for grass pollen, tree pollen and allergy to insect stings. With pollen allergy, the treatment involves a series of injections given over 3 weeks before the pollen season each year, for 3 years. Subcutaneous immunotherapy has been shown to be very effective and is suitable for the most severe cases of hayfever. Unfortunately, it is possible to have quite severe allergic reactions to the injections especially in children and adults with asthma. This treatment is thus not suitable for asthmatics and is also only given under careful supervision, with each injection followed by a 1 hour period of observation.
- Sublingual Immunotherapy: Recent advances have meant that immunotherapy can now be given without injections. Instead, the allergen extract is given under the tongue either by tablets or drops. This method is very safe and severe reactions are extremely rare although the first dose of treatment is still given under careful supervision in the hospital. This makes it a more suitable treatment for asthmatics, as long as their asthma is well controlled. Whilst sublingual immunotherapy avoids the need for injections it does need to be taken on a daily basis either all year or through the whole pollen season for a total of 3 years. Importantly, in both adults and children, it has been shown that a 3 year course of treatment has an effect that can last for years after the treatment has finished, confirming that it has a long term impact on the immune system. As it is a newer treatment, there is less information regarding how long the beneficial effects last after the end of treatment and how well it prevents the development of asthma, but large studies have strongly suggested a meaningful preventative effect.
Our doctors will discuss with you which type of immunotherapy may be best suited for you. Once a decision has been reached, you will be provided with more detailed information about the particular type of treatment.
Food desensitisation is an area of increasing interest and we are already using this in our practice (eg for peanut, milk and egg allergy) and more information can be found here.
Professor Adam Fox
Date reviewed: March 2021
Adam Fox is a Professor of Paediatric Allergy with over 20 years experience in both the NHS and private sector. Professor Fox is Commercial Medical Director at Guy’s & St Thomas’ Hospitals NHS Foundation Trust and Professor of Paediatric Allergy at King’s College London and the founding Director of the KCL Allergy Academy, a postgraduate educational programme, which was a finalist at the BMJ Awards in 2018.
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