Anaphylaxis to Vaccines
Mary S. Hayney, PharmD, MPH, FCCP, BCPS
Anaphylaxis following immunization is very rare—about one case per 1.5 million doses of vaccine. However, immunizing pharmacists must be ready to respond quickly with each immunization, because anaphylaxis can occur without warning at any time. Classic anaphylaxis is mediated by a class of antibodies called immunoglobulin E. In such cases, the individual was exposed to one or more antigens in a vaccine dose earlier in life and became sensitized. However, the allergen does not have to be in the same form at reexposure. For example, an individual who is truly allergic to eggs (a rare situation) may have had an exposure to eggs in his/her diet and then experience an anaphylactic reaction when receiving an influenza vaccine.
Screening for History of Anaphylaxis
Anaphylaxis is a medical emergency. Anaphylaxis is a rapid-onset, progressive, clinical syndrome involving at least two organ systems. The combination of cardiac, respiratory, and skin or mucosal symptoms are most specific. Cardiorespiratory symptoms are required for a diagnosis of anaphylaxis. Rhinitis, hives, or asthma symptoms alone are not sufficient for anaphylaxis diagnosis. Individuals may report an “allergy” to a vaccine or excipients that may not be a contraindication to immunization. For example, sensitivities to latex or neomycin often consist of contact dermatitis. Individuals who can eat eggs generally can receive an influenza vaccine safely.