[Allergic reactions and vaccines: distinguishing true and false reactions].

Similarly to other medications, vaccines may be responsible of allergic reactions. However, IgE-mediated allergies are extremely rare. The diagnosis of allergies to a vaccine is complex and these allergies are often over-diagnosis due to fear of severe anaphylaxis. Indeed, most of the patients labelled as allergic to a vaccine may tolerate a subsequent injection of the vaccine without clinical reaction. The economic impact and the impact on health, both from an individual point of view but also in terms of public health, are very important. Before this diagnosis can accurately be made, a complete work up is essential. If an allergy workup is necessary, it will be primarily based on skin tests.