This document summarizes research on the growing diversity of H3N2 influenza A virus in US swine and its impact. It finds that the H3 subtype is evolving into multiple genetic clusters with evidence of reassortment. Antibody studies show inconsistent cross-reactivity between clusters, which may impact vaccine effectiveness. Nearly 350 human cases of influenza from exposure to infected fair pigs have been reported since 2005, primarily in children. Continued genetic monitoring, timely vaccine updates, and partnerships across animal and human health are needed to minimize the impact.