Vaccine associated enhanced respiratory disease (VAERD) has been described in pigs vaccinated with whole-inactivated influenza virus (WIV) and subsequently challenged with heterologous influenza A virus (IAV). Pathological changes in lungs of pigs with VAERD include significant lymphocytic infiltration and increased levels of proinflammatory cytokines. To better identify the mechanism(s) associated with VAERD versus partial-protection we defined the lymphocyte populations infiltrating the lungs following challenge, as well as level of complement activation. Pigs partially protected against infection had an increase in IFN-g producing memory T cells (CD4+CD8α+ double-positive), while pigs with VAERD had an increase in IFN-γ producing CD4 and CD4-CD8α- double-negative T cells compared to non-vaccinated, challenge controls. Additionally, IL-17A and complement activation was significantly higher in the lungs of pigs experiencing VAERD. These data suggest a role for the inflammatory IL-17A response and complement activation in the development of VAERD pathology, as well as differential activation of T cell populations.