Ethical consideration
The study was approved by the Institutional Review Board (IRB) of the
Research Institute for Tropical Medicine (RITM) in Muntinlupa City,
Philippines. Individual consent forms were waived since archived samples
were used in this study. Permission was sought from the Philippine
National Influenza Centre (PNIC) to access the samples and data
respectively. The samples were devoid of any identifiers that may lead
to the patient.