Cytomegalovirus-associated accumulation of late-differentiated CD4 T-cells correlates with poor humoral response to influenza vaccination

► Influenza vaccination is less effective in CMV-seropositive elderly than young. ► CD8+CD28− T-cells are not associated with poor humoral vaccine responses. ► CD45RA+CCR7−CD27−CD28−CD4+ T-cells accumulate in CMV-seropositive individuals. ► CD45RA+CCR7−CD27−CD28−CD4+ cells are associated with poor humoral vaccine responses.