Disease severity	Feeding, hydration, conscious state	Respiratory and vital signs	Oxygen requirement †
Mild	Normal or mildly reduced feeding	No or mild upper respiratory tract symptoms, OR No or mild work of breathing	No supplemental oxygen required to maintain SpO2 > 92%
Moderate	Poor feeding, unable to maintain hydration without nasogastric or intravenous fluids, AND Normal conscious state	Moderate work of breathing, OR Abnormal vital signs for age (tachycardia, tachypnoea) but does not persistently breach early warning (eg, MET) criteria, ‡ OR Brief self‐resolving apnoea (infants)	Requires low flow oxygen (nasal prongs or mask) to maintain SpO2 > 92%
Severe	Poor feeding, unable to maintain hydration without nasogastric or intravenous fluids, OR Drowsy or tired but easily rousable	Moderate to severe work of breathing, OR Abnormal vital signs for age (tachycardia, tachypnoea) with breaches of early warning (eg, MET) criteria, OR Apnoea needing support or stimulation (infants)	Requires high flow oxygen at 2 L/kg/min § to maintain SpO2 > 92%
Critical	Poor feeding, unable to maintain hydration without nasogastric or intravenous fluids, OR Altered conscious state or unconscious	Unable to maintain breathing or prevent apnoea without advanced modes of support, OR Abnormal vital signs for age with persistent breaches of early warning (eg, MET) criteria, OR Haemodynamically unstable without inotropic or vasopressor support, OR Other organ failure	Requires advanced modes of support to maintain oxygenation: ► high flow nasal oxygen at > 2 L/kg/min, § OR ► non‐invasive ventilation, OR ► intubation and mechanical ventilation, OR ► extracorporeal membrane oxygenation

MET = medical emergency team; Spo ₂ = peripheral oxygen saturation.

^*Depending on the physical size and/or developmental status of the patient, either the paediatric or adult severity grading can be applied.

^†Oxygen saturation targets should be modified for patients with cyanotic heart disease.

^‡Temperature instability should be considered an abnormal vital sign in infants. Fever is common in children and does not contribute to determination of illness severity in isolation.

^§Infants and neonates < 4 kg may be managed on high flow nasal cannula oxygen at 2–8 L/min irrespective of weight. Comorbidities (eg, preterm infants, oncology, immunosuppressed etc) may increase the risk of more severe disease.