Table 1 Operationalization of commonly used case-definitions

• Severe acute lower respiratory infection: hospitalized children who had cough or difficulty breathing (i.e., having tachypnea, or oxygen requirement) with retractions [3]

• Severe acute respiratory infection: hospitalized children with subjective fever and cough [27]

• Influenza-like illness: children who had sought care in emergency room with subjective fever and cough [22]