D3.292 - Safety profile of the yellow fever vaccine in egg-allergic children

Yellow fever remains a potentially severe disease of major epidemiological relevance in Brazil, with ongoing viral transmission and reported mortality rates of up to 56%. As the vaccine is produced in embryonated chicken eggs and may contain residual ovalbumin, concerns persist regarding its administration in egg-allergic children, the second most common food allergy worldwide. This study aims to evaluate the safety of the yellow fever vaccine in this population.

A retrospective analysis (2016-2025) was conducted including children with egg allergy and delayed vaccination who had been referred to a specialized outpatient clinic. Egg-allergy reactions were classified according to type and intensity, and immunological tests were described. Based on risk stratification, patients were either referred back to primary care or vaccinated under supervision with full or a fractional dose. Adverse events after supervised vaccination were analyzed.

Of the 545 patients included, 77% were under 2 years and 52% were male. Most egg reactions were classified as cutaneous (n = 332; 61%), including urticaria, rash, or angioedema. Specific IgE to egg white was reported in 219 patients (76%), with 119 (54%) positive results. Specific IgE to ovomucoid was measured in 90 patients (31%), with 35 positive results. No statistically significant correlation was observed between egg-allergy reaction and positive IgE. Supervised vaccination was recommended in 270 (49.5%) cases, of which 242 received the full dose and 28 received a fractionated dose. Prick test and intradermal test with the vaccine component were performed in 5 patients (0.9%), all of whom had negative results. Only five immediate adverse events occurred after supervised vaccine, all classified as mild. A part of the vaccinated patients was assessed for delayed reactions (n = 98; 36%), with only 16% of them reporting mild cutaneous or gastrointestinal symptoms or fever.  All improved spontaneously or after symptomatic treatment at home, without a need of medical evaluation. Of all 61 patients who had a previous history of egg-induced anaphylaxis, only four experienced mild immediate reaction. No severe adverse events were reported.

The yellow fever vaccine was considered safe in egg-allergic patients of all severities. To avoid unnecessary delays in vaccination, only patients with severe IgE-mediated reactions following egg exposure should be referred to specialized care.