Influenza A virus A/PR/8/34 (PR/8) was grown in 10-day-old SPF Premium Eggs (Charles River SPAFAS. North Franklin, CT) and prepared as described previously [3] . Contemporary influenza H3N2 virus, A/New York/238/2005 (NY/238), was created by reverse genetics using plasmids that corresponded to the consensuses sequence obtained from a human swab specimen collected in New York State in the winter of 2005 [23] . NY/238 was passaged in Madin-Darby Canine Kidney (MDCK) cells and the viral titer was measured by plaque assay on MDCK cells as described previously [34] . Briefly, stocks of purified virus was serially diluted in DMEM with 1 mg/ml TPCK trypsin (Sigma-Aldrich, St. Louis, MO) and used to inoculate triplicate wells of near confluent MDCK cells. After a 1 h inoculation, the inoculum was removed and the cells were overlaid with MEM with 4% FBS and 0.5% SeaKem LE agarose (Cambrex, Rockland, ME). Plaques were stained and counted after 72 h incubation at 37uC, with the agarose overlay medium containing 10% neutral red (Sigma-Aldrich). For UV-inactivation of PR/8 or NY/238, 500 ml diluted virus was placed in a 35-mm 2 petri dish on ice and irradiated twice in a UV Stratalinker (Stratagene, La Jolla, CA) at a cumulative dose of 120 mJ/cm 2 . Viral inactivation was demonstrated by plaque assay on MDCK cells as described above.