Immediate Hypersensitivity Reaction Related to Rabies Post-Exposure-Prophylaxis in Thailand with Subsequent Rabies Vaccine Change to Avoid Polygeline Vaccine Excipient with Successful Challenge and Treatment Tolerance in the United States

BACKGROUND: Untreated rabies is fatal, globally killing 60,000 persons/years. Rabies vaccine (RV) is life-saving, of various types and used in high-risk rabies exposure (HRRE) as a post-exposure prophylaxis (PEP) series of initial (RV-i) and completion (RV-c) doses. Polygeline has been implicated in immediate allergic reactions to tick-borne encephalitis vaccine and is an excipient in Rabipur, a purified chick embryo vaccine (PCECV) as part of Thai Red Cross (TRC) RV protocol. In United States, RVs are Rabavert (PCECV), containing polygeline, and Imovax Rabies, a human diploid cell vaccine (HDCV) that does not. RV-associated adverse reactions occur up to 6% as mostly non-IgE/skin-limited or immune complex and rarely nonfatal anaphylaxis. We describe TRC-RV-immediate allergic reaction in a male child traveling in Thailand and how after his return to United States , we were able to overcome RV-PEP delays and demonstrate safe treatment tolerance with a different RV. METHODS: Review of literature, Thai/US RV and Allergy Protocols, Pink Book/RV Inserts RESULTS: A healthy 4-years old US boy had HRRE from feral cat bite in Thailand with immediate disseminated hives at 1 hour post-TRC-RVi (Day 0), resolved with oral antihistamine. Upon US return (Days 3-8), clinicians stopped RV-PEP due to RV allergy fears; Day 6 rabies-immunoglobulin given. On Day 9, US academic Allergist/Infectious Disease referral done: no other medical problems found; HDCV skin prick test (negative); TRC-RV (not available); two-step HDCV-RV challenge performed (10%, then full); Days 13 and 20, HDCV-RV-c full tolerated; Days 30+, asymptomatic; serum tryptase 3.2 ng/ml; Rapid Fluorescent Foci Inhibition Test (RFFIT) CONCLUSION: RV type I hypersensitivity reactions are uncommon, components to RVs vary worldwide and such adverse RV reactions should not stop RV-PEP. Analysis of vaccine content, exposures, and relevant testing is critical to deducing likely reaction type and candidate antigens as excipients in non-RVs and across RV types. IgE-vaccine tests may not be reliable/possible and mid-series RV change to non-polygeline type may be a viable option when RV-c must be done to reach timely RV-c-PEP treatment tolerance and avoid hypersensitivity reactions. DISCLOSURES: All authors: No reported disclosures.