Verbal consent for the initial diagnostic testing of these samples for respiratory viruses, including influenza, was obtained from the parents of these children. Such verbal (rather than written) consent is routine for such standard diagnostic tests in Hong Kong. The local Joint Chinese University of Hong Kong-New Territories East Cluster (Joint CUHK-NTEC) Research Ethics Committee institutional review board awarded ethics approval for this retrospective sequencing and molecular epidemiological study (study reference number: CRE-2005.390) without the need to obtain further, explicit, written consent. This is also in agreement with the American College of Epidemiology guidelines [33] for such retrospective epidemiological/surveillance studies.