CD8A and infection: However, the number of activated HLA-DR expressing CD4+ and CD8+ T cells was significantly higher in ChAdOx1 nCoV-19 animals three days after SARS-CoV-2 challenge (p = 0.0039 and p = 0.0010 respectively), indicating that ChAdOx1 nCoV-19 vaccination had advanced the kinetics of the adaptive T cell-mediated response to infection.