Inclusion Criteria: 

• Admission to PICU or SDU at any point during illness due to severity (not due to bed availability).
• ≤ 21 years old on admission.
• Influenza-associated LRTI:
  • Positive influenza test (rapid antigen, DFA or PCR) ;and
  • > 1 sign of acute respiratory illness: cough, shortness of breath, tachypnea or retractions, invasive or non-invasive mechanical ventilation, need for FiO2 to maintain SpO2 >92%, pulmonary infiltrate or hyperinflation on chest imaging.
• At least 1 parent or legal guardian able and willing to provide permission.

Exclusion Criteria:

• Previous enrollment in this study during the current season.
• Hospital acquired influenza infection as determined by site hospital infection control experts.
• Pre-existing conditions that are known risk factors for severe influenza infection (with the exception of asthma or reactive airways disease (RAD).  Exclusions include:
  • Chronic pulmonary (except asthma/RAD) or upper airway disorders;
  • History of prematurity in patients < 1 year of age;
  • Known immune disorders;
  • Cardiac disease with compromise requiring medications or alterations in activities;
  • Neurologic disorders impairing respiratory muscle strength or secretion management;
  • Sickle cell disease;
  • Complex genetic disorders impairing multiple organ systems; AND
  • Metabolic disorders that may be worsened by infection including diabetes mellitus.