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 supine or in head-down 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 supine or in head-down 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