Version July 2025
| Anaphylaxis | Acute stress response | ||
| General | Vasovagal reaction with syncope | ||
| Onset | Usually 5 min after immunization but may be delayed up to 60 min. | Sudden, occurs before, during, or shortly after (<5 min) immunization. | Sudden, occurs before, during, or shortly after (<5 min) immunization. May present after 5 min if the individual stands suddenly. |
| System | |||
| Skin | Generalized urticaria (hives) or generalized erythema, angioedema (localized or generalized), generalized pruritus with or without skin rash, generalized prickle sensation, localized injection-site urticaria, red and itchy eyes. | Pale, sweaty, cold, clammy. | Pale, sweaty, cold, clammy. |
| Respiratory | Persistent cough, noisy breathing, and airway constriction (wheeze, stridor). If very severe, respiratory arrest. | Hyperventilation (rapid, deep breathing). | Normal to deep breaths. |
| Cardiovascular | Increased heart rate, decreased blood pressure, circulatory arrest. | Increased heart rate, normal or increased systolic blood pressure. | Decreased heart rate with or without transient decrease in blood pressure. |
| Gastrointestinal | Nausea, vomiting, abdominal cramps. | Nausea. | Nausea, vomiting. |
| Neurologic and other symptoms | Uneasiness, restlessness, agitation, loss of consciousness, little response when supine or lying flat. | Fearfulness, lightheadedness, dizziness, numbness, weakness, tingling around the lips, spasms in hands and feet. | Transient loss of consciousness, good response once supine or lying flat, with or without tonic-clonic seizure. |
