The influenza vaccine contains an inactivated live influenza virus. The virus is grown in chick extraembryonic allantoic fluid. The greatest amount of egg measured in the influenza vaccine is 0.7 μg per 0.5 mL of vaccine.
6 Most manufacturers list the content of ovalbumin in the package insert. However, the concentration of ovalbumin may differ from year to year and from 1 brand of vaccine to another (
Figure).
6,7 On the basis of results in previous studies, vaccine lots containing less than 1.2 μg/mL of oval-bumin have been tolerated well by egg-hyper sensitive individuals. Data regarding the least concentration of egg in the influenza vaccine that will cause an adverse reaction remain unclear.
Recent recommendations by the US Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices (ACIP) state that the influenza vaccine can be administered to egg-hypersensitive patients without any precautions.
8 If the patient can ingest lightly cooked eggs (eg, scrambled eggs) without reaction, he or she may receive the vaccine per usual protocol. If the patient develops hives only after ingesting eggs or egg-containing products, they may receive the vaccine but with a 30-minute observation period after the immunization. If any systemic events occur after the ingestion of egg, the the patient should be referred to a physician with expertise in managing allergic conditions for further evaluation before immunization. The ACIP recommendations differ from those made by other organizations—including the American Academy of Allergy, Asthma, and Immunology; the American College of Allergy, Asthma, and Immunology; the Joint Council of Allergy, Asthma, and Immunology; and the National Institute of Allergy and Infectious Diseases—which recommend using split dosing in patients who have had anaphylactic events after ingesting eggs.
8,9
The influenza vaccine administered nasally contains 2000 μg of gelatin per 0.2-mL dose, compared to 250 μg of gelatin per 0.5-mL dose when administered intramuscularly.
4 Physicians administering this vaccine should be aware of the signs and symptoms of anaphylaxis and have appropriate medications available for treatment.