Background:

Yellow fever vaccine (YFV) induces weaker immune responses in HIV-infected individuals. However, little is known about YFV responses among antiretroviral-treated patients and potential immunological predictors of YFV response in this population.

Methods:

We enrolled 34 antiretroviral therapy (ART)-treated HIV-infected and 58 HIV-uninfected adults who received a single YFV dose to evaluate antibody levels and predictors of immunity, focusing on CD4+ T-cell count, CD4+/CD8+ ratio, and Human Pegivirus (GBV-C) viremia. Participants with other immunosuppressive conditions were excluded.

Results:

Median time since YFV was nonsignificantly shorter in HIV-infected participants than in HIV-uninfected participants (42 and 69 months, respectively, P= 0.16). Mean neutralizing antibody (NAb) titers was lower in HIV-infected participants than HIV-uninfected participants (3.3 vs. 3.6 log 10 mIU/mL, P= 0.044), a difference that remained significant after adjustment for age, sex, and time since vaccination (P= 0.024). In HIV-infected participants, lower NAb titers were associated with longer time since YFV (rho:− 0.38, P= 0.027) and lower CD4+/CD8+ ratio (rho: 0.42, P= 0.014), but not CD4+ T-cell count (P= 0.52). None of these factors were associated with NAb titers in HIV-uninfected participant. GBV-C viremia was not associated with difference in NAb titers overall or among HIV-infected participants.

Conclusions:

ART-treated HIV-infected individuals seem to have impaired and/or less durable responses to YFV than HIV-uninfected individuals, which were associated with lower CD4+/CD8+ ratio, but not with CD4+ T-cell count. These results supports the notion that low CD4+/CD8+ ratio, a marker linked to persistent immune activation, is a better indicator of functional immune disturbance than CD4+ T-cell count in patients with successful ART.