Figure legends:
Figure 1. Sample collection and plan of analyses.
Figure 2. Monthly H3N2 seropositive and virus isolation rate in 6,532 sets of paired nasal swabs and pig sera, 2012-2016.
Figure 3. Maximum likelihood phylogenetic tree of 174 concatenated genomes of H3N2 swine influenza viruses in 2012-16. The tree was constructed using IQ-TREE and branch supports were obtained with SH-aLRT test. Strain name is followed by pig tattoo codes and sampling date. Scale bar is given in numbers of substitutions per site and branch support aLRT statistics are shown at major nodes with value ≥ 0.8.