Administration of yellow fever vaccine in patients with egg allergy

Background: The population of large parts of Africa, South America and travellers to these areas are at risk of yellow fever (YF) with a 50% mortality risk. Yellow fever vaccine (YFV) propagated in hens' eggs confers protection in 95% of the vaccinated. The rate of anaphylaxis for YFV ranges from 0.42 to 1.8/100,000 doses with most cases considered to be due to egg allergy. Egg allergy is a contraindication for the YFV. Nevertheless, the potential fatal sequelae from YF give the incentive to protect everyone at risk irrespective of their allergic status.

Methods: Six subjects who had had a recent reaction to egg and who were travelling to endemic areas (3 adults and 3 children) underwent skin prick tests (SPT) with undiluted YFV and egg extract. Intradermal tests for YFV were undertaken at a 1:10 dilution. In 4 egg-allergic patients with a positive SPT to YFV, a 7-step desensitization protocol was used. A 2-step (10 + 90%) protocol was used in the 2 subjects with a negative YFV SPT. Premedication was not administered.

Results: All 6 patients were successfully vaccinated. Four patients completed desensitization: 1 developed mild local erythema at the injection site, 1 had fleeting generalized urticaria with local erythema/angioedema and 2 did not experience any adverse reactions. Patients who received YFV in 2 steps developed no adverse reactions.

Conclusions: We describe the successful administration of YFV in 6 egg-allergic patients. The Cambridge Allergy 7-step protocol allows for its safe administration in patients with positive SPT to YFV. A 2-step protocol can be used in patients with negative YFV SPT.