Immunotherapy for allergies

What it is

Every other allergy treatment works downstream of the problem. Antihistamines block the effects of histamine once it has been released; steroid sprays damp down the inflammation that follows. The allergy itself is unchanged, and the treatment has to be repeated indefinitely.

Immunotherapy, also called desensitisation, is the exception. Gradually increasing doses of the allergen are given over a long period, and the immune system slowly stops treating it as a threat. The aim is to change the response rather than to suppress it.

It is not new or experimental. It has been in clinical use for more than a century, and modern extracts are far more purified than early ones.

What it is for, and what it is not for

This is the part worth reading before anything else, because immunotherapy is reserved for a narrow set of situations rather than offered for allergy in general.

It is used for:

• severe reactions to wasp or bee stings, including anaphylaxis
• severe hay fever that has not responded to ordinary medication
• house dust mite allergy causing year-round rhinitis
• some animal allergies, where avoidance genuinely is not possible — occupational exposure in veterinary or laboratory work, for instance

It is generally not used for:

• people allergic to many things at once — treating more than two allergens is unusual
• eczema or urticaria
• animal allergy where the animal is staying in the house, since the exposure continues regardless
• minor sting reactions, such as local swelling
• most people with asthma, particularly severe asthma, though there are exceptions

Asthma and high blood pressure need to be stable before starting, and beta blockers may have to be changed, because they interfere with the treatment of a severe reaction should one occur.

Two routes

The old picture of immunotherapy is a course of injections. That is still one option, and for some allergies the only one, but it is no longer the whole story.

Subcutaneous immunotherapy is the injection route, given into the upper arm. It starts with frequent doses while the amount is built up, then settles into a maintenance injection every few weeks. Each one is followed by a wait in the clinic, usually an hour. It is the route used for wasp and bee venom allergy.

Sublingual immunotherapy is a tablet, drops or spray held under the tongue, taken daily. The first dose is given in a specialist clinic, after which it continues at home. It has a better safety record than injections and suits people who cannot face needles or cannot make repeated hospital trips.

The catch with the sublingual route is that it depends entirely on taking it. Missed doses undermine it, and a daily tablet for three years asks more of someone's consistency than a monthly appointment does.

Which route is available depends on the allergen. The range of licensed products in the UK is narrow and changes, so what can actually be offered is a question for the specialist rather than something to settle in advance.

How long it takes

Longer than most people expect, and the figure is worth knowing before committing.

Three years is the standard course in the UK, and some run to five. Stopping early raises the chance of the allergy returning, so the duration is part of the treatment rather than a target to beat.

Improvement is gradual. Six months is a realistic minimum before much is noticeable, and usual medication continues in the meantime rather than being abandoned at the start.

What it can actually achieve

The honest answer varies a great deal by allergen, and lumping them together is how overclaiming happens.

For venom allergy the figures are striking: protection against serious reactions runs at around 98% for wasp stings and roughly 90% for bee stings. For someone who has had anaphylaxis from a sting, that is a change in how safe it is to be outdoors.

For hay fever and dust mite allergy the realistic promise is substantially reduced symptoms and a reduced need for medication, with the benefit persisting for years after the course ends. That is a worthwhile outcome. It is not usually the complete disappearance of the allergy, and anyone told to expect a cure has been oversold.

Getting it in the UK

Immunotherapy is a specialist treatment. It is not prescribed in general practice and it is not bought over a counter.

The route in is a GP referral to an allergy clinic, which may involve travelling, since specialist allergy services are unevenly distributed. Assessment usually involves skin prick testing, sometimes blood tests, and a review of general health. Waiting lists are common.

The constraint, in other words, is access rather than cost — which is the opposite of how American material on this subject frames it.

Safety, and why the hour in the waiting room matters

The treatment works by giving someone the thing they are allergic to. The risk follows directly from that.

Reactions do happen. Around one in ten people receiving venom immunotherapy has a reaction at some point during the course. This is why it is given only where anaphylaxis can be treated immediately, and why the wait after an injection is not a formality.

More ordinary side effects are common and manageable: itching or swelling at the injection site, which can build over hours; tiredness or a flu-like feeling for a few hours afterwards; mild irritation in the mouth with the sublingual route, which usually fades over the first weeks. Avoiding alcohol and hard exercise on injection days reduces them.

Food allergy is a separate story

Older accounts state flatly that immunotherapy cannot be used for food allergy because the risk of anaphylaxis is too great. That was the position, and it has moved.

Desensitisation for food allergy — peanut in particular — is an active field, and it works by the oral route rather than by injection. In the UK it is currently available privately rather than as standard NHS treatment.

It is also not a cure. Someone successfully desensitised to peanut is protected against an accidental exposure rather than freed to eat peanuts, and the treatment has to be maintained. It is a specialist conversation, not something to arrange independently.

One timing point

Pollen immunotherapy cannot be started during the pollen season. It has to begin several months beforehand, which in practice means that someone whose hay fever is unbearable in June needs to have raised it the previous autumn or winter.

Given the referral waits on top of that, anyone considering it is better off starting the conversation in the months when their symptoms are least troubling — which is, inconveniently, exactly when it is easiest to forget about.