A 25-year-old woman presented to an infectious diseases (ID) physician with a 4-day history of symptoms following receipt of a quadrivalent influenza vaccine. Two hours after receiving the vaccine, the patient experienced abdominal pain. One hour later, she felt warm and developed diffuse urticaria and rigors. Because of her worsening condition, she presented to the emergency department, where she was given intravenous methylprednisolone 40 mg, ondansetron 8 mg, diphenhydramine 25 mg, and normal saline. Her urticarial rash resolved within 45 minutes, and she was discharged home.
Three days later, she sought additional medical care because of persistent chest tightness, new-onset bronchospasm, pleuritic chest pain, nausea, diarrhea, facial swelling, urticaria, and anorexia. The patient’s vital signs were within normal limits. The oropharynx lacked erythema or obstruction. The lungs were clear to auscultation bilaterally, and heart sounds were regular, with no ectopy or murmurs. Her abdomen was soft, nontender, and nondistended. The patient demonstrated dermatographism on her back.
Historically, the patient had received the influenza vaccine without difficulty. She tolerated latex but had concerns about egg allergy due to vomiting with egg-yolk exposure.
The ID physician, suspecting anaphylaxis and sustained allergic response to the influenza vaccine, arranged for immediate follow-up with an allergist. Multiple tests were done. A negative result on epicutaneous testing to egg was inconsistent with an immunoglobulin (Ig) E-mediated food allergy.
Intradermal testing with the flu vaccine (diluted 1:100) was subsequently performed with appropriate controls. A positive intradermal result is typically a wheal ≥ 5 mm larger than the control. The patient had a 5-mm/15-mm wheal-and-flare response to the flu vaccine, compared to a negative response to saline (FIGURE). (Since the vaccine did not contain gelatin, this was not tested.)
Based on the positive response to flu vaccine and negative response to egg, it was determined that the patient had experienced an anaphylactic reaction to the vaccine itself.
In adults, the most common adverse reactions to quadrivalent flu vaccine include pain, headache, and fatigue. IgE-mediated reactions to the influenza vaccine, especially anaphylactic reactions, are rare. A Vaccine Safety Datalink study found 10 cases of anaphylaxis after more than 7.4 million doses of inactivated flu vaccine were given, for a rate of 1.35 per 1 million doses.1
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