The incidence of anaphylactic or severe allergic reactions to vaccines is very low, less than one case per million vaccine doses. Larger studies from later years report no deaths. The cause of the reaction is usually not the immunizing antigen itself, but rather some other vaccine ingredient such as egg protein from the production process or gelatin added as a stabilizer. Most people with egg allergy can be vaccinated without any reaction. Vasovagal reactions with or without hyperventilation are common after vaccination. They can be rather dramatic and are often mistaken for anaphylactic reactions. Correct diagnosis is important in making it possible to vaccinate those who might otherwise run the risk of serious infections.