Virus samples were collected from both the apical and basolateral surfaces at multiple time points. Apical washing and harvesting was performed by adding 200 ml of PBS to the apical chamber, incubating the samples for 10 min at 37uC and 5% CO 2 , and removing and storing the 200 ml of PBS from the apical chamber. Thereafter, 50 ml of medium were collected from each basolateral chamber.