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- Material and methods
Background: In a previous controlled study, we demonstrated that preseasonal grass pollen immunotherapy for 3 years was effective in children. Moreover, a significant clinical benefit could still be observed 6 years after discontinuation of specific immunotherapy (SIT). In the current study, we examined the same group of patients again to investigate whether there is a prolonged benefit 12 years after SIT is stopped.
Methods: Twenty-two patients with previous SIT (from 1989 through 1991) or standardized seasonal pharmacotherapy only were prospectively followed during the grass pollen season of 2003. Primary end points were symptom score, medication use, and combined symptom and medication score. In addition, skin prick test reactivity, development of new sensitizations, and prevalence of seasonal asthma were evaluated.
Results: Total hay fever symptom score (P < 0.03), use of medication (P < 0.05), and combined symptom and medication score (P < 0.03) remained lower in patients with previous SIT when compared with the control group. Decreased immediate skin response to grass pollen returned 12 years after cessation of SIT. The percentage of new sensitization, however, continued to be significantly smaller in patients with previous SIT (58%) compared with the controls (100%, P < 0.05). There was a tendency for lower prevalence of seasonal asthma in the post-SIT group (P = 0.08).
Conclusion: This prospective controlled prolonged follow-up study demonstrates the ongoing clinical benefit 12 years after discontinuation of SIT. Furthermore, the reduction in onset of new sensitization, which was found 6 years after discontinuation of SIT, is sustained 6 years later.
New data demonstrate the efficacy of specific immunotherapy (SIT) not only as a therapeutic agent but also as a preventive strategy to reduce onset of new sensitization to nonrelated allergens (1–3), progression from allergic rhinitis to asthma (4, 5), and to improve long-term outcome of already established asthma (3, 6).
However, only limited knowledge exists about the duration of the preventive and therapeutic effects after discontinuation of SIT. The main objectives of this study were to evaluate whether grass pollen SIT in childhood is still effective 12 years after discontinuation and to test whether the reduced onset of new sensitization is prolonged.
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- Material and methods
The present study assesses two groups of patients 15 years after enrolment for grass pollen SIT or standardized seasonal pharmacotherapy alone. To our knowledge it is the longest follow-up study of grass pollen SIT. The data demonstrate an ongoing clinical benefit 12 years after cessation of 3-year preseasonal SIT with grass pollen allergoids in childhood in terms of both a reduction of hay fever symptoms and use of medication for symptom relief. Furthermore, the reduction in development of new sensitizations to perennial allergens, which has been observed 6 years after cessation of SIT (3), is sustained also in the longer term.
Only a few papers have addressed the long-term effects of grass pollen SIT (3, 5, 8–12). Most studies demonstrate prolonged clinical benefit and some show decreased immunologic reactivity for 3–6 years after discontinuation of SIT. The majority has been performed in adults (5, 8–12) and some of them were not controlled (5, 8). There is evidence that immunologic reactivity begins to return after 1–3 years (8, 10, 12). In our patients, recurrence of immediate skin reactivity to allergen occurred later than 6 years after cessation of SIT. However, increased reactivity to grass pollen was not accompanied by an increase of symptoms.
Changes in immunologic parameters and provocation tests may be of interest in elucidating mechanisms, but cannot replace clinical evaluation (13). The only parameter estimating clinical efficacy of SIT are reduction in symptoms and use of medication. However, individual patient behavior during the pollen season may be different. Some are using more medication for rapid symptom relief. Others may have decreased symptom perception and subjectively underestimate symptom severity. The addition of weekly combined symptom and medication scores may partly compensate for individual patient behavior. However, a shortcoming of all immunotherapy studies remains that there is currently no objective means to monitor clinical efficacy of SIT.
An important finding of recent studies is the reduction in onset of new sensitization to nonrelated allergens after SIT. Our data are in accordance with the results of two studies performed in children monosensitized to house dust mites. A significant reduction in development of new IgE-mediated sensitization was observed 3 years after SIT when compared with controls (1, 2). Patients in the present study were observed for a longer period suggesting that onset of new sensitization is not delayed by SIT but may be permanently reduced.
Limitations of the current follow-up study are the small number of subjects and the fact that the original study had no run-in phase and was not double-blind placebo controlled. However, a study design requiring placebo injections in a randomized group of children over prolonged time is difficult to justify. It is also important to note that the selection of patients is essential for outcome of SIT. The observed beneficial long-term effects may not be translated to subjects having a broad spectrum of sensitizations. For example, SIT with multiple allergens was not effective in asthmatic children sensitized to seasonal and perennial allergens (14). Nevertheless, we believe that our results are of importance because more knowledge is needed about the long-term allergen-specific and unspecific immunomodulatory effect of early intervention by SIT in childhood.
In conclusion, this prospective controlled long-term follow-up study demonstrates that both the clinical efficacy and the preventive capacity of grass pollen SIT, observed at the 6-year follow up, is still evident 12 years after discontinuation of SIT when compared with seasonal pharmacotherapy alone.