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Table. Clinical features that may help differentiate between a vasovagal episode and anaphylaxis

Clinical feature Vasovagal episode Anaphylaxis
Onset
  • Immediate, usually within minutes of, or during, vaccine administration
  • Usually within 15 minutes of vaccine administration, but can occur within hours
Respiratory symptoms or signs
  • Normal breathing; may be shallow, but not laboured
  • Cough
  • Wheeze
  • Hoarseness
  • Stridor
  • Signs of respiratory distress, such as abnormally rapid breathing (tachypnoea), cyanosis or rib recession
  • Upper airway swelling (eg lip, tongue, throat, uvula, larynx)
Cardiovascular symptoms or signs
  • Bradycardia
  • Weak/absent peripheral pulse
  • Strong carotid pulse
  • Hypotension — usually transient and corrects in supine position
  • Loss of consciousness — improves once in a lateral recumbent position
  • Tachycardia
  • Weak/absent carotid pulse
  • Hypotension — sustained and no improvement without specific treatment (Note: In infants and young children, limpness and pallor are signs of hypotension)
  • Loss of consciousness — no improvement once in a lateral recumbent position
Skin symptoms or signs
  • Generalised pallor
  • Cool, clammy skin
  • Pruritus (skin itchiness)
  • Generalised skin erythema (redness)
  • Urticaria (weals)
  • Angioedema (localised or general swelling of the deeper layers of the skin or subcutaneous tissues)
Gastrointestinal symptoms or signs
  • Nausea or vomiting
  • Abdominal cramps
  • Diarrhoea
  • Nausea or vomiting
Neurologic symptoms or signs
  • Person feels faint or light-headed
  • Person has a sense of severe anxiety and distress

Note: Anaphylaxis features are modified from The Brighton Collaboration Case Definition Criteria for Anaphylaxis.6 Neurologic symptoms are not listed in this case definition.6 However, symptoms of anxiety and distress, including feelings of impending doom, are reported in people experiencing anaphylaxis.9

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Vaccination procedures
After vaccination

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