Thank you for your inquiry.
I think that it is certainly reasonable for patients to ask this question, and certainly desirable for us to be able to give a simple answer. However, in my opinion, no such answer is available.
As you will see from the abstracts copied below, there is a great deal of heterogeneity in individual responses to immunotherapy using the same allergen for the same disease, and in addition, there is a great deal of heterogeneity depending upon the allergen employed, the disease treated, the severity of the disease, et cetera. Thus, I personally am not able to extract from a review of the available literature any simple answer to your question.
There are 14 Cochrane reviews of this issue, and a number of other meta-analyses. I have only sent you two examples of the Cochrane reviews (one for asthma and the other one is for rhinitis) as well as one other meta-analysis for asthma. As you can see, the complexity of the issue, just from these abstracts, does not allow for us to give a simple answer in terms of percentages. These references also give you a link to the Cochrane reviews if you would like to see if you are able, upon reading these reviews, to extract a simple answer yourself.
As noted, I have not been able to do so in answer to the same questions posed by my patients. I can therefore only tell you what I normally tell patients when I am presented with this question.
I simply state that the studies in the literature show that this therapy is effective in the majority of patients, and that the range of effectiveness can vary significantly from patient to patient, but it is a known, accepted, and proven treatment. Unfortunately, we cannot tell who will respond and who will not before starting the therapy, and we cannot tell to what degree that response will occur. We can only state that thousands of patients have been treated over the years, and that the treatment has stood the test of time with the results showing that treated patients consistently do better overall than those who do not receive this treatment.
Unfortunately, as noted, I do not think we can give specific percentages as a reflection of the reality of the issue.
Thank you again for your inquiry and we hope this response is helpful to you.
American Journal of Respiratory and Critical Care Medicine [1995, 151(4):969-974]
A meta-analysis of clinical trials of allergen immunotherapy was undertaken to assess the efficacy of this controversial form of therapy in asthma. A computerized bibliographic search revealed 20 randomized placebo controlled double-blind trials of allergen immunotherapy for asthma. The results extracted included asthmatic symptoms, medication requirements, lung function, and bronchial hyperreactivity (BHR). Categorical outcomes were expressed as odds ratios and continuous outcomes as effect sizes. The combined odds of symptomatic improvement from immunotherapy with any allergen were 3.2 (95% CI 2.2 to 4.9). The odds for reduction in medication after mite immunotherapy were 4.2 (95% CI 2.2 to 7.9). The combined odds for reduction in BHR were 6.8 (95% CI 3.8 to 12.0). The mean effect size for any allergen immunotherapy on all continuous outcomes was 0.71 (95% CI 0.43 to 1.00), which would correspond to a mean 7.1% predicted improvement in FEV1 from immunotherapy. Although the benefits of allergen immunotherapy could be overestimated because of unpublished negative studies, an additional 33 such studies would be necessary to overturn these results. Allergen immunotherapy is a treatment option in highly selected patients with extrinsic ("allergic") asthma.
Allergen immunotherapy for the treatment of chronic asthma Abramson MJ, Puy RM, Weiner JM
Background: Allergen specific immunotherapy has long been a controversial treatment for asthma. Although beneficial effects upon clinically relevant outcomes have been demonstrated in randomised controlled trials, there remains a risk of severe and sometimes fatal anaphylaxis. The recommendations of professional bodies have ranged from cautious acceptance to outright dismissal. With increasing interest in new allergen preparations and methods of delivery, we updated the systematic review of allergen specific immunotherapy for asthma.
Objectives: The objective of this review was to assess the effects of allergen specific immunotherapy for asthma.
Search strategy: We searched the Cochrane Airways Group Trials Register up to 2005, Dissertation Abstracts and Current Contents.
Selection criteria: Randomised controlled trials using various forms of allergen specific immunotherapy to treat asthma and reporting at least one clinical outcome.
Data collection and analysis: Three authors independently assessed eligibility of studies for inclusion. Two authors independently performed quality assessment of studies.
Main results: Eighty-eight trials were included (13 new trials). There were 42 trials of immunotherapy for house mite allergy; 27 pollen allergy trials; 10 animal dander allergy trials; two Cladosporium mould allergy, two latex and six trials looking at multiple allergens. Concealment of allocation was assessed as clearly adequate in only 16 of these trials. Significant heterogeneity was present in a number of comparisons. Overall, there was a significant reduction in asthma symptoms and medication, and improvement in bronchial hyper-reactivity following immunotherapy. There was a significant improvement in asthma symptom scores (standardised mean difference -0.59, 95% confidence interval -0.83 to -0.35) and it would have been necessary to treat three patients (95% CI 3 to 5) with immunotherapy to avoid one deterioration in asthma symptoms. Overall it would have been necessary to treat four patients (95% CI 3 to 6) with immunotherapy to avoid one requiring increased medication. Allergen immunotherapy significantly reduced allergen specific bronchial hyper-reactivity, with some reduction in non-specific bronchial hyper-reactivity as well. There was no consistent effect on lung function. If 16 patients were treated with immunotherapy, one would be expected to develop a local adverse reaction. If nine patients were treated with immunotherapy, one would be expected to develop a systemic reaction (of any severity).
Authors' conclusions: Immunotherapy reduces asthma symptoms and use of asthma medications and improves bronchial hyper-reactivity. One trial found that the size of the benefit is possibly comparable to inhaled steroids. The possibility of local or systemic adverse effects (such as anaphylaxis) must be considered.
Immunotherapy by allergen injections for seasonal allergic rhinitis ('hay fever') Calderon MA, Alves B, Jacobson M, Hurwitz B, Sheikh A, Durham S
Seasonal allergic rhinitis ('hay fever') is a global health problem and its prevalence has increased considerably in the last two decades. Treatment includes allergen avoidance, drugs such as antihistamine tablets and nasal sprays, and immunotherapy (vaccination). For those patients whose symptoms remain uncontrolled despite drug treatment, specific allergen immunotherapy (SIT) is advised. Specific allergen immunotherapy is most commonly administered as subcutaneous (under the skin) injections by specialists requiring a building-up period followed by a maintenance period of three to five years. Immunotherapy may also be delivered by the oral, nasal or sublingual route and these will be studied in separate Cochrane reviews, as will immunotherapy for perennial (all year round) allergic rhinitis. In this review we aimed to evaluate the efficacy and safety of injection immunotherapy, compared with placebo, for reducing symptoms and the need for medication. We identified randomized, double-blind, placebo controlled trials of specific allergen immunotherapy in patients with seasonal allergic rhinitis due to tree, grass or weed pollens. Fifty-one studies satisfied our inclusion criteria. In total there were 2871 participants (1645 in the treatment groups and 1226 in the placebo), each receiving on average 18 injections. The duration of treatment varied from three days to three years. This review has shown that injection immunotherapy in suitably selected patients with hay fever results in significant reductions in symptom scores and medication use. Injection immunotherapy has a known and relatively low risk of severe adverse events. We found no long-term consequences from adverse events and no fatalities.
Phil Lieberman, M.D.