There was no evidence for an association between CD4 or CD8 T cell count and YFV immunogenicity (multiplicative effect per 10% increase 1.05, 95% CI 0.91–1.20, p = 0.469, and 0.95, 95% CI 0.86–1.04, p = 0.295, respectively) or between Human Pegivirus co-infection and YFV immunogenicity among HIV-infected individuals (fold change 0.65, 95% CI 0.09–4.47, p = 0.659, Table 4). Here, CD4 is linked to coinfection.