Don’t blame eggs. It was previously believed that reactions to the flu vaccine were due to egg allergies, because the vaccine may contain a tiny amount of ovalbumin, a protein found in egg. However, multiple studies have supported the safety of injectable influenza vaccine in patients with an egg allergy because the amount of ovalbumin contained in each dose is very low and thus not likely to evoke an allergic response.2,3
How and when to test for allergy. For patients who have a severe allergic reaction or anaphylaxis after immunization, immediate-type allergy skin testing should be performed by an allergist to establish whether the reaction was IgE mediated and to determine the causative agent.
It’s best to wait 4 to 6 weeks after an anaphylactic reaction before doing skin testing, as earlier testing can lead to false-negative results.4 The vaccine should first be tested by using the prick method. If this test is negative, an intradermal test with the vaccine diluted 1:100 should be performed with appropriate controls.5
Should the patient receive future vaccinations?
If skin testing is positive, there are several ways to proceed. A vaccine to which the patient has previously had an allergic reaction and positive skin test can still be administered, with caution.5 With emergency supplies, medication, and equipment immediately available, medical personnel can administer the influenza vaccine in titrated doses. If the full vaccine dose is normally a volume of 0.5 mL, the patient is first given 0.05 mL of a 1:10 dilution and then, at 15-minute intervals, given full-strength vaccine at doses of 0.05, 0.1, 0.15, and finally 0.2 mL, for a cumulative dose of 0.5 mL.5
Alternatively, the patient can forego the vaccination, although this decision has its own risks. In a patient who has previously had an anaphylactic reaction but has negative skin tests—meaning it is unlikely that the patient has IgE antibody to the vaccine—the vaccine can be administered and followed with an observation period of at least 30 minutes.5z Our patient was counseled on both options and decided to forego the vaccine.
THE TAKEAWAY
Anaphylaxis is a life-threatening allergic reaction requiring immediate treatment. Anaphylaxis after vaccine receipt is exceedingly rare.6 Most IgE-mediated allergic reactions post vaccination are attributed to added or residual substances in the vaccine, rather than the immunizing agent itself.6 While common local reactions and fever post vaccination do not contraindicate future vaccination, rare anaphylactic reactions need to be further evaluated, with a referral to an allergist to determine if the patient is, in fact, allergic to additive ingredients within the vaccine vs allergic to the vaccine itself.
CORRESPONDENCE
Kathleen Dass, MD, 24601 Coolidge Highway, Oak Park, MI 48237; kathleen.j.dass@gmail.com