In the HTS, all NTSs were collected by a trained HCP at home visits on days 1, 4, and 7 after recruitment. Nasal swabs were collected by inserting and rotating a sterile plain swab (viscosetipped collection swab with a snappable plastic stick; EURO-TUBO) into the anterior nares, and throat swabs were collected by rubbing a second sterile swab against the tonsillar fossa. Both swabs were then snapped off into a tube containing viral transport medium (0.5% bovine serum albumin in Earle's balanced salt solution with antibiotic). Specimens were stored in an insulated transport container with at least 2 ice packs immediately after collection. Specimens were then either delivered directly or first stored overnight in a study outpatient clinic in a 2°C-8°C refrigerator and then delivered the next day to the central testing laboratory at Queen Mary Hospital by courier in ice boxes.