Patients with a history of probable egg allergy and candidates for receiving the H1N1 vaccine were referred to the pediatric and adult allergy and immunology clinics for administration of the H1N1 vaccine. A patient was labeled as egg allergic if they had a convincing clinical history of an IgE mediated reaction to egg ingestion (including symptoms of urticaria, angioedema, cough, other breathing difficulties, wheeze, pruritus, flushing, rhinoconjunctivitis, throat tightness, gastrointestinal complaints, cyanosis, and circulatory collapse) within 2 hours. They either had positive epicutaneous testing to egg white allergen and/or were immunocap positive to egg as part of confirming the clinical diagnosis.
The Canadian Society of Allergy and Clinical Immunology (CSACI) recommends administration of the H1N1 vaccine based on 2 risk categories of patient with egg allergy . The first category are lower risk patients(with mild gastrointestinal or mild local skin reaction, tolerating ingestion of small amounts of egg, or positive skin/specific IgE test to egg without knowingly exposed to egg) or higher risk (previous respiratory or cardiovascular reaction, generalized hives or those with poorly controlled asthma). For lower risk patients the vaccine is recommended to be administered with a 60 minute observation period. For patients at higher risk, or if the risk is unknown, an initial test dose with 10% of the total dose followed by 30 minutes of observation. If there is no reaction after 30 minutes, the remaining 90% of the vaccine can be given with observation for 60 minutes. Children who tolerate the split dose and who require a second dose (first time receiving influenza vaccine) can receive the next dose in one injection. For all of the patients in this study, it was decided that if a skin test was found to be negative, the entire dose of the vaccine would be given with a 30 minute observation period.
Patients were skin tested to the H1N1 vaccine in the outpatient pediatric and adult allergy and immunology clinics of the Health Sciences Centre and Children's Hospital of Winnipeg, Manitoba, Canada. Upon determination of a negative skin test, the vaccine was administered with a 30 minute observation period. Children under 9 years of age were administered 1.88 μg's of hem-agglutinin antigen per 0.25 ml dose and individuals ≥ 9 years were administered 3.75 μg's of hemagglutinin antigen per 0.5 ml dose intramuscularly based on the above protocol. Control subjects consisted of patients with no history of egg allergy, who were referred to the allergy and immunology clinics due to various reasons including a history of a previous reaction to the influenza vaccine.
Epicutaneous testing was performed via the prick lanceter method using egg white extract (ALK Abelló), AREPANRIX H1N1 AS03 Adjuvanted H1N1 vaccine (GlaxoSmithKline), along with a positive (histamine) and negative (saline) control (ALK Abelló). A mean wheal diameter of 3 mm or greater than elicited by the negative control was considered positive. The ovalbumin content of the AREPANRIX H1N1 AS03 Adjuvanted H1N1 vaccine used had a stated allowable limit of 165ng/ml.