Background: Venom immunotherapy (VIT) protects most patients allergic to Hymenoptera stings while booster injections are continued. Few data on long-term protection after discontinuation of treatment are available.
Objective: We sought to investigate protection from re-stings over a prolonged period after stopping VIT.
Methods: Re-sting data were obtained from 200 of 322 patients in whom VIT had been stopped between 1988 and 1992 after a duration of at least 3 years. The 25 (12.5%) patients who again developed systemic allergic reactions were compared with 50 matched patients without re-sting reactions. Clinical data and diagnostic parameters (i.e., skin sensitivity and specific IgE and IgG) were studied.
Results: Of the 25 patients who had re-sting reactions, 19 had been treated with bee venom (relapse rate, 15.8%), and six had been treated with Vespula venom (relapse rate, 7.5%). About half of the re-sting reactions occurred on the first resting after stopping VIT. Most of these reactions were mild, whereas the majority of reactions occurring after repeated re-stings were severe. When re-sting reactions were related to the total re-stings per year, an accumulation of sting reactions was observed in years 3 to 5 after stopping VIT. Patients with re-sting reactions had been receiving VIT for a significantly shorter duration (43.35 months) than those with continued protection (54.65 months) (p < 0.01). Of the diagnostic parameters, only a negative intracutaneous skin test at 10(-3) gm/L predicted long-term protection reliably.
Conclusion: Venom immunotherapy of 3 to 5 years duration induces long-term protection in most patients. In rare occasions severe re-sting reactions may, however, occur, especially after repeated re-stings.