Randomization will be clustered by residence hall since it is likely that incidence of influenza infection will be correlated among subjects within residence halls. In year 2, clustering was done by residence house to increase the clustering units. The intervention residence halls will receive one of the following two interventions: (i) masks alone or (ii) masks plus alcohol-based hand sanitizers (62% ethyl alcohol) and hygiene education. The remaining halls will serve as comparison units. The control dorms will be similar to the intervention dorms on basic demographic distributions, such as age range and geographical proximity. Residence halls that are randomized to the control arm will not receive any masks, hygiene education materials, or alcohol-based hand sanitizer.