CD8A and influenza: Changes in the ratio were found to be the result of an increase in CD8+ T-cell populations, specifically, CD27−, CD28−, CD56+, and CD57+, CD45RA+, and CD45RA+/RO+ cells (13), markers that indicate reduced effector functionality and provides support for the finding of poor humoral response to influenza vaccination in those with a low CD4:CD8 ratio (169).