D2.163 - Effectiveness and safety of Venom ImmunoTherapy (VIT) with “Rapid Cluster” induction protocol

Current guidelines propose various protocols for the induction phase of Venom ImmunoTherapy (VIT) in patients with hymenoptera venom allergy. These protocols, proven to be both effective and safe, often require extended timeframes, up to 15 weeks, to reach the maintenance phase; such lengthy protocols may reduce therapy compliance for some patients. This led us to the development of the "Rapid Cluster" protocol.

The "Rapid Cluster" protocol involves a first session (day 0) where 15.5 mcg of hymenoptera venom is administered in four separate injections. This is followed by a second session (day 7) during which 50 mcg is administered in two injections, and a third session (day 14) where the maintenance dose of 100 mcg is reached in two injections.

We analyzed patient data from the Hymenoptera Venom Allergy Clinic at “Ca’ Foncello” Hospital in Treviso who began VIT using the "Rapid Cluster" protocol from March 2020 to the present.

During the follow-up period, we collected data on the type of hymenoptera triggering the allergic reaction, any adverse reactions to VIT, and the effects of potential re-stings.

A total of 150 patients were included in the study (28 patients for Apis mellifera venom allergy, 32 for Vespa crabro venom, 39 for Polistes spp. allergy, 49 for Vespula spp. venom, and 2 for Polistes and Vespula venom). Among the 150 patients, 7 were diagnosed with mastocytosis.

During the induction phase, 17 adverse reactions (11.3%) were recorded, including 16 localized reactions of varying severity (edema, itching and/or pain at the injection site) and one systemic reaction (hypotension) that required adrenaline administration. The induction scheme was modified in 9 patients. No patients discontinued the induction phase.

During the follow-up period, 68 patients (45.3%) experienced a re-sting, and among these, only 3 patients (4.41%) developed a systemic reaction: one grade III-anaphylaxis reaction and two grade IV reactions. For the latter, we doubled the administered venom dose, also because the reactions were induced by a sting from the same hymenoptera for which they were already undergoing VIT. None of the re-stung patients required intensive care.

The "Rapid Cluster" VIT induction protocol proved to be safe, with a lower incidence of systemic reactions compared to literature data, and effective, as evidenced by the near absence of severe adverse reactions following re-stings.

Further studies are needed to assess the efficacy during the maintenance phase.