As the question of how long VIT should last in order to provide long-term protection is a long-standing issue, we evaluated the specific venom IgE decrease throughout 5-years-long VIT in three groups of yellow jacket (YJ) venom-allergic patients: stung during the first three years of VIT (SP3), during the last two years (SP5) and patients not stung (NS).
Methods:
We retrospectively evaluated 232 patients submitted to 5-year-long VIT. Specific venom IgE levels were determined at the baseline, after 3 and 5 yrs of VIT (CAP method, Phadia, Italy). All stung patients were clinically protected.
ANOVA analysis evaluated differences among CAPs and in each CAP value among the three groups. MANOVA multivariate analysis evaluated differences in overall CAPs and the effects of age, gender, Mueller grade and stings number. A p<0.05 was considered statistically significant. Data were analysed by ‘SPSS®’ 13.0 (SPSS Inc., Chicago, IL).
We called NS patients to check if they were stung after VIT discontinuation.
Results:
We selected 84 NS, 72 SP3 and 76 SP5 patients.
Specific YJ-IgE levels decreased during VIT, as CAPs are statistically different at time 0, 3 and 5 (p<0.001).
Considering CAP levels at the first control (CAP3), NS patients presented lower values than SP3 patients (p=0.002); no significant difference was found between NS and SP5 patients. At the last control (CAP5), CAP values of NS and SP5 patients were different (p=0.002) as well as between SP3 and SP5 patients (p=0.014). No significant difference was found between NS and SP3 patients.
By MANOVA, IgE decrease was inversely correlated with Mueller grade (p=0.012) and age (p=0.002).
We recalled all NS patients by phone, 7/84 (8.3%) patients related one well tolerated sting, as they did not develop any allergic reaction.
Conclusions:
In everyday practice if a patient never stung during VIT fulfils the temporal criterion, but specific IgE are not negative, a decrease of IgE levels ranging from 57 to 70% in respect to baseline might be a satisfactory parameter for stopping VIT.
As a further confirmation of our conclusions, even if not statistically significant, all not stung patients were clinically protected after VIT discontinuation.