100665 - Omalizumab Enables Safe Honeybee Venom Immunotherapy in a Patient with Systemic Reactions to Immunotherapy

Background

Honeybee venom immunotherapy (VIT) is the only disease-modifying treatment forHymenoptera venom allergy. However, systemic reactions during VIT may jeopardize itscontinuation, creating a critical dilemma in high-risk patients in whom discontinuation is not asafe option. Omalizumab has emerged as an adjuvant strategy to improve tolerability inselected cases.

Case report

A 26-year-old woman, with moderate intellectual disability since early childhood andpermanent rural exposure, experienced her first systemic reaction to honeybee sting in2017. She subsequently presented multiple life-threatening anaphylactic reactions to Apismellifera. Baseline laboratory evaluation revealed total IgE 297 kU/L and specific IgE to Apismellifera 93.8 kUA/L. Sensitization to Vespula spp (5.57 kUA/L), Polistes spp (1.06 kUA/L),and Vespa crabro (12.30 kUA/L) was also detected. Baseline serum tryptase was withinnormal range and REMA score was 1, indicating low risk for clonal mast cell disease.

Two previous attempts at honeybee VIT were discontinued due to systemic reactions at lowdoses, including generalized erythema and one episode of hypotension with urticariaconsistent with anaphylaxis. Given her cognitive impairment and inability to self-administeremergency treatment, definitive protection through VIT was considered mandatory.

Omalizumab 450 mg subcutaneously every 4 weeks was initiated in 2020. After 3 months ofanti-IgE therapy, honeybee VIT was reintroduced using a conventional build-up schedule.The patient tolerated reinitiation without local or systemic reactions. Combined treatmentwith omalizumab and VIT was maintained for 4 years. Throughout the entire vaccinationperiod, she did not experience any systemic or significant local reactions. Both VIT andomalizumab were discontinued at the end of 2024 after completing a full 4-year course. Nofield re-stings have occurred since VIT initiation.

Conclusions

● This case highlights that omalizumab can enable safe reintroduction and long-termcontinuation of honeybee venom immunotherapy in patients with prior systemicreactions to VIT.

● In high-risk individuals in whom treatment discontinuation is unsafe, anti-IgE therapymay represent a decisive strategy to achieve sustained protection against life-threatening anaphylaxis.