The treatment of patients allergic to insect stings with insect-venom injections has been shown to be 97 percent effective in reducing the risk of sting-induced anaphylaxis. However, the frequency of systemic reactions to subsequent stings in unimmunized adults with previous reactions is approximately 60 percent. To determine which factors, in addition to a history of reaction and evidence of venom-specific IgE antibody, predispose patients to future insect-sting reactions, we studied a venom-sensitive group of children who were deemed to be at relatively low risk for severe reactions; 28 percent of them received venom therapy.

We studied 242 children, 2 through 16 years of age, each of whom had had a systemic allergic reaction, affecting only the skin, to an insect sting. Each child had a positive skin-test reaction to one or more of five hymenopteran venoms. Sixty-eight children received immunotherapy with insect venom and 174 did not; about half were randomly assigned to treatment groups, and the rest were assigned on the basis of the patient's (or the parents') choice. The results of accidental stings during four years of observation were evaluated.

In the treated group, 84 stings in 36 patients resulted in one systemic reaction (1.2 percent of stings). In contrast, 196 stings in 86 untreated children resulted in 18 systemic reactions (9.2 percent of stings, P<0.001). Sixteen of these 18 reactions were judged to be milder than the patient's reaction to the first sting, 2 were similar in severity, and none were more severe.

These data confirm that immunotherapy with insect venom prevents recurrences of systemic reactions after subsequent insect stings. Because of the surprisingly low rate of reactions among untreated children, we could not identify any characteristics that were predictive of repeat reactions. Since only 9.2 percent of stings in the untreated children led to a systemic reaction and since there was no progression to a more severe reaction, we conclude that venom immunotherapy is unnecessary for most children who are allergic to insect stings. (N Engl J Med 1990; 323:1601–3.)