Persistence of efficacy after a brief course of polymerized ragweed allergen: a controlled study

Immunotherapy with PRW has been demonstrated to be safe and effective. To determine whether the efficacy would remain in successive ragweed seasons without further therapy, a trial was conducted comparing PRW to histamine placebo therapy in patients that had received courses of PRW previously. Those patients were also compared to previously untreated ragweed-sensitive patients. In a double-blind fashion, 21 previously treated patients were treated before the 1982 ragweed season with four injections of PRW therapy, whereas 21 previously treated patients were treated with four injections of placebo therapy. An additional control group of 21 previously untreated ragweed-sensitive patients received no injections. Daily symptom and medication score sheets were completed by patients each day of the ragweed season. Blocking antibody rose elevenfold with treatment (p less than 0.0001) in the PRW group. There was a statistically significant difference in symptom score mean between untreated patients (1007 +/- 174) and previously treated patients whether they received supplemental injections (554 +/- 180) (p less than 0.01) or whether they did not (650 +/- 168) (p less than 0.03). In summary the efficacy of 15 injections of PRW immunotherapy persists at least several years without need for supplemental immunotherapy.