Phylogenetic tree based on nucleotide sequence of the entire hemagglutinin gene of five H3N2 viruses detected in Study 1 and relevant standards representing original cluster IV H3N2 viruses, six subgroups within cluster IV (A–F), and recent uncategorized H3N2 Ontario viruses. The tree is built using Neighbor-Joining method and its reliability is estimated using 1000 bootstraps. Note that standard names have been shortened and modified so that the end of the name after underscore represent the cluster number (IV), or subgroup designation (A–F). The study viruses are labeled with the pig identification number, followed by sampling number. The scale represents number of substitutions per site.