Two cohorts of approximately 650 pigs, one pre-vaccination and one postvaccination, were monitored throughout their time in the nursery by collecting 30 individual nasal swabs and pen oral-fluid samples (16 oral-fluid samples total) at 4, 6, 8, and 10 weeks of age. Each pen-based oral-fluid sample represented 30 to 40 pigs. The cohorts were conveniently selected so that the pre-vaccination cohort was moved out of the nursery prior to the arrival of the postvaccination cohort. The objective of longitudinal monitoring was to determine the prevalence over time of influenza virus in the nursery pre- and post vaccination.