Anorexia; Anaphylactic reaction to the vaccine itself; This literature case was received on 15-Feb-2022 and concerned a 25-year-old, female patient.  This literature case report described a case of the patient who experienced an anaphylactic reaction to the vaccine itself.  The patient's concurrent conditions were not reported. She tolerated latex but had concerns about egg allergy due to vomiting with egg-yolk exposure. The patient's concomitant medications were not reported. The patient's historical vaccine included influenza vaccine (brand not specified) and the patient had no difficulty after receiving it.  On an unspecified date, the patient was vaccinated with quadrivalent influenza virus vaccine polyvalent (brand not specified, dose, route of administration, anatomical location: not reported) for influenza immunisation. The batch number was not reported.   On the same day, two hours after receiving influenza virus vaccine polyvalent, the patient experienced abdominal pain. One hour later, the patient felt warm and developed diffuse urticaria and rigors. Because of her worsening condition, she was presented to the emergency department, where she was given intravenous methylprednisolone at a dose of 40 mg, ondansetron at a dose of 8 mg, diphenhydramine at a dose of 25 mg and normal saline. Her urticarial rash resolved within 45 minutes and she was discharged home.  On an unspecified date, three days later, the patient sought additional medical care because of persistent chest tightness, new-onset bronchospasm, pleuritic chest pain, nausea, diarrhoea, facial swelling, urticaria, and anorexia. The patient's vital signs were in normal limits. The oropharynx lacked erythema or obstruction. The auscultation bilaterally revealed that the lungs were clear and heart sounds were regular with no ectopy or murmurs. Her abdomen was soft, nontender, and nondistended. The patient demonstrated dermatographias on her back. The infectious diseases (ID) physician suspected anaphylaxis and sustained allergic response to the influenza vaccine and arranged for immediate follow-up with an allergist.   On an unspecified date, multiple tests were done. Epicutaneous testing to egg revealed a negative result which was inconsistent with an immunoglobulin (Ig) E-mediated food allergy. Intradermal testing with the flu vaccine (diluted 1:100) with appropriate controls revealed a 5-mm/15-mm wheal-and-flare response to the flu vaccine, compared to a negative response to saline (positive intradermal result is typically a wheal > or equal to 5 mm larger than the control).  The patient developed a wheal in response to flu vaccine but not to egg, saline, or histamine. 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.  The outcome of the events of anaphylactic reaction to vaccine and anorexia were not reported.  The authors assessed the events as related to influenza virus vaccine polyvalent. The patient experienced an anaphylactic reaction to the vaccine itself. Also, the patient decided to forego the vaccine in the future.  The event of anaphylactic reaction to vaccine was considered to be medically significant by a Physician within Seqirus' Pharmacovigilance and Risk Management Department.  In conclusion, anaphylaxis is a life-threatening allergic reaction requiring immediate treatment. Anaphylaxis after vaccine receipt is exceedingly rare. Most IgE-mediated allergic reactions post vaccination was attributed to added or residual substances in the vaccine, rather than the immunizing agent itself. 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.    Company comment: A 25-year-old patient experienced anaphylactic reaction and anorexia within three days after receiving the suspect product influenza virus vaccine polyvalent. Reportedly, two hours after vaccination the patient developed abdominal pain as well as nausea three days after vaccination. The patient's medical history and concomitant drugs were not provided. Although confounding factors (abdominal pain and nausea) contributed to the development of the event anorexia, causal role of the suspect product cannot be totally excluded, therefore causality for that event is assessed as possibly related, due to plausible chronology. Based on suggestive temporal relationship (reportedly within three hours), causality for the event anaphylactic reaction is assessed as possibly related.; Reporter's Comments: The patient experienced an anaphylactic reaction to the vaccine itself. Also, the patient decided to forego the vaccine in the future.; Sender's Comments: A 25-year-old patient experienced anaphylactic reaction and anorexia within three days after receiving the suspect product influenza virus vaccine polyvalent. Reportedly, two hours after vaccination the patient developed abdominal pain as well as nausea three days after vaccination. The patient's medical history and concomitant drugs were not provided. Although confounding factors (abdominal pain and nausea) contributed to the development of the event anorexia, causal role of the suspect product cannot be totally excluded, therefore causality for that event is assessed as possibly related, due to plausible chronology. Based on suggestive temporal relationship (reportedly within three hours), causality for the event anaphylactic reaction is assessed as possibly related.