ART-mediated recovery of the CD4 T cell count or the CD4:CD8 T cell ratio was shown to associate with a higher magnitude of post-vaccination antibody levels for influenza15, hepatitis B16,17, hepatitis A18, tetanus and diphtheria toxoid19 and with higher PBMC IFNγ responses after influenza vaccination20. Here, CD4 is linked to hepatitis A virus infection.