CD27 and influenza: Importantly, our multivariable analysis of early Day 3 variables associated with peak Day 28 influenza-specific HAI and/or VNA antibody response demonstrated negative associations between the percentage of CD8+CD28low T cells (for HAI), as well as the percentage IgD+CD27- naïve B cells, percentage overall CD20- B cells and plasmablasts (at Day 3), and peak antibody titers.