Safety of yellow fever vaccine administration in confirmed egg-allergic patients.

Yellow fever vaccine (YFV) is recommended in endemic areas but represents a risk for egg-allergic patients, as it is cultivated in embryonated eggs. This study aims to describe the outcomes of yellow fever vaccination in patients with confirmed egg allergy (EA). Methods:A prospective study was conducted from January 2018 to September 2019. EA was diagnosed through positive oral food challenge (OFC), recent history of anaphylaxis following egg contact (anaphylaxis in the last 6 months) or immediate allergic reaction in the last 2 months with positive specific IgE. A skinprick test (SPT) with YFV was performed. If the SPT was negative, an intradermal test (ID) was performed at a 1:100 dilution. If the ID was negative, a full dose of YFV was administered. If the skin prick test or ID were positive, the YFV was administered using a graded dosing protocol. Results: It was included 58 patients with confirmed egg allergy (36 M:22F), with a median age of 2.3 years (0.7-13.9 y/o). Forty-two patients had a positive OFC. Nine reported recent anaphylaxis. The other 7 had reactions in the last 2 months with positive specific IgE. During OFC, 15 presented anaphylaxis, while the other 27 presented hives and/or angioedema or vomiting. SPT with YFV was negative in all patients. ID was negative in 48 patients who uneventfully received a full dose of YFV. Ten patients had a positive ID and received YFV in graded doses. Six patients presented a mild reaction controlled with antihistamines, and 4 patients received the vaccine without reactions. Positive ID was significantly related to the vaccine reaction (p < 0.0001). Administration of YFV using a specific protocol was safe even in anaphylactic patients. However, we recommend performing the ID, which can help predict a higher risk of vaccine reaction. An appropriate setting is required to control adverse events.