Immunotherapy - a treatment for severe allergies

What is Immunotherapy?

Immunotherapy (IT) is a well-established treatment for certain severe allergies. Increasing doses of allergen are administered until an allergic person can tolerate allergen exposure without developing major symptoms. IT may be referred to in lay terms as "desensitisation" though this is not strictly correct, because it is rare for patients to lose their allergy completely under treatment. "Hyposensitisation" is more accurate.

In the UK, IT is generally reserved for patients with the most severe allergies and for certain types of allergy. The reason for this policy is that the treatment is quite intensive and has some side effects. If simple treatments are effective then there is no need for IT. In addition IT should only be used for allergies where it has been proved to be effective.

Will I benefit from immunotherapy?

Patients with certain allergies may be considered for IT:

1. Life-threatening reactions to wasp or bee stings

Sudden collapse (Anaphylactic shock) or Other life-threatening reactions.

Venom IT is highly effective:

• 98% protection against serious wasp venom reactions
• 80% protection against serious bee venom reactions

An alternative treatment is to carry injectable Epinephrine (adrenaline), but this is not always a complete treatment or "antidote" and further medical aid may be necessary after a sting.

Minor reactions, such as swelling at the site of the sting, or nettle rash (urticaria), can be treated simply.

Avoidance of stings:

• Avoid eating out of doors
• Be extra careful around refuse bins
• Do not walk barefoot or in sandals on grass or in country areas
• Do not wear perfumes or other scented products
• Use insect repellents
• Carry insecticide cream in the car
• Do not drink out of cans

If you have had allergic reactions to wasp or bee stings, an Allergy specialist's advice may be helpful in deciding whether IT is necessary as the classification of reactions is complex.

There is no vaccine available for mosquito bites which rarely, if ever, cause generalised allergic reactions.

2. Severe hayfever

Normally, hayfever can be successfully controlled by treatments such as nasal sprays, antihistamines and eyedrops. Some people find these treatments ineffective. In this situation a short course of steroid tablets may be needed.

Strategy for avoidance of severe hayfever:

Start full protective treatment well before the pollen season starts.

• Regular steroid nasal spray.
• Regular sodium cromoglycate or nedocromil sodium eyedrops.
• Regular steroid inhaler, if you have asthma.
• Antihistamine tablets as required.

Once symptoms are established, it can be much harder to control the allergic reaction.

If you have tried the preventive approach outlined above and still need steroid tablets or injections or had severe hayfever symptoms during the season, then you may be a candidate for pollen IT.

3. Animal Allergies

Avoidance of the allergen is most important. If you keep pets to which you are allergic at home, you will not be considered for IT as it is unlikely to succeed when there is a background of continuous allergen exposure causing allergic inflammation.

Most people who occasionally come into contact with animal allergens can treat themselves successfully by taking antihistamines and inhalers prior to contact with the pet. For instance, if going to a friend's house where pets are kept, treatment should be started 30-60 minutes beforehand.

IT may be indicated when a highly allergic individual is unable to control symptoms by this strategy
and for those who react to tiny quantities of allergen brought into the home on others clothes or
property. An Allergy specialist's advice is essential in this circumstance, to determine the contribution of the allergen exposure to allergic symptoms. Occupational exposure, such as in veterinary surgeons
or nurses, or in patients whose job involves visiting peoples homes, may also be considered for treatment.

Conditions for which immunotherapy is unhelpful

Multiple allergies: it is unusual for patients to receive IT for more than two allergies.

There are no preparations available for IT treatment of food allergy.

Allergic rashes such as eczema and nettle rash cannot be treated with IT.

What does immunotherapy treatment involve?

Screening at an allergic clinic

If you and your doctor think that you may need IT, you will need to be referred to an Allergy Specialist. In some areas, this may mean travelling some distance, perhaps to a teaching hospital.

You will be asked to have some allergy tests: skin test and sometimes a blood test for allergic antibodies.

You will also need a physical examination to assess your general fitness. It is important that conditions such as uncontrolled high blood pressure and asthma are stabilised prior to commencing treatment. It is sensible to get such problems sorted out before attending the Allergy clinic, if possible.

If you are taking a beta blocker for any reason, you will need to discuss changing this for an alternative treatment.

If you have asthma...

Few asthmatics will be considered for immunotherapy. In general, the more severe your asthma, the less likely that you will be considered for IT. This may seem unfair but the reason is that allergic reactions to immunotherapy are most dangerous in asthma because of the respiratory complications which may occur.

However, there are exceptions. Asthma which occurs only in the pollen season is not a problem for pollen IT as the induction phase (when there is greatest risk of reactions) will be outside the season. Asthmatics will not be turned down for bee and wasp venom IT either, because the risk of a life-threatening reaction to a sting outweighs the risk of any reactions during immunotherapy. However, it is important that asthma control is carefully maintained to reduce risks.

If the specialist thinks that you need treatment...

You may have to join a waiting list.

Pollen IT cannot be started during a pollen season. If your hayfever is uncontrolled by standard treatment now, you may need a course of steroids from your doctor.

Ask about Allergy referral just after a pollen season to ensure that waiting lists do not reduce your chances of treatment for the following year. Treatment will need to be started several months in advance of the next pollen season.

Injections

IT is currently given as injections of purified allergen extracts, under the skin of the upper arm. The schedule may vary at different hospitals.

In the induction phase, injections will be given at intervals of a week or less, while allergen doses are gradually increased. Once on the maintenance dose, you will be asked to continue attending for injections every few weeks for at least 2 years.

Individual responses vary and the duration of your treatment will be tailored to your needs. Skin tests and blood tests may be used to help determine how effective your treatment is.

"Rush" immunotherapy is a rapid method of reaching the maintenance dose. Several injections may be given a day and sometimes this will require admission to hospital. Usually, immunotherapy is given in clinics and you are only required to wait for one hour after the injection. Rush IT is only given in exceptional circumstances as allergic reactions to this treatment are more common.

You will be asked to wait in the clinic for one hour after each injection so that if serious side effects occur they can be rapidly treated.

Itching and swelling are common reactions at the injection site, although many patients experience no reaction at all. For some patients swelling can increase over hours to days after the injection. Antihistamine tablets and an ice pack will help ease the swelling in this situation.

Some treatments require attendance for maintainance injections every few weeks for around three years. There are some pollen vaccines which may be given for a few weeks before the season each year.

Any reactions occurring after one hour are less specific and do not need urgent treatment. Some patients feel tiredness or flu-like symptoms over the hours following an injection. Avoiding alcohol or strenuous activities on the day of the injection reduces the risk of side effects like these.

Is immunotherapy dangerous?

There has been serious reactions to immunotherapy in the past. In 1986 it was decided that IT should only be carried out in specialist centres where full emergency services were available.

Since that time, IT has had a good safety record. The allergen extracts are more highly purified nowadays and are administered only by highly experienced specialists in a safe environment.

Authors: Cecilia Trigg and Lawrence Youlten, Department of Allergy and Respiratory Medicine, Guy's Hospital London SE1 9RT