[Vaccine-induced urticaria: how to differentiate allergy (IgE) from pseudoallergy?]

The occurrence of allergic-type manifestations during the course of vaccination is relatively common, and in the majority of cases, these are benign reactions which are also known as "pseudoallergy". They are not immunological in nature and do not activate the effectors of specific immunity.

The aim of our work was to propose a practical diagnostic approach following an immediate and/or accelerated post-vaccination accident.

We report our experience in four adults who were referred for urticaria which appeared following vaccination and in two children who were allergic to eggs and were referred for assessment before administration of vaccines containing egg proteins.

The immunoallergological examinations (prick-test and intradermal tests with immediate reading) confirmed the absence of immediate hypersensitivity to the vaccine in question and all the patients could be vaccined without incident.

The majority of post-vaccination reactions with an allergic appearance is benign and do not contra-indicate further vaccination. If there is a suspicion of a true IgE dependent allergy, an immunoallergological investigation will differentiate true allergy from pseudoallergy.