The 17D live attenuated yellow fever (YF) vaccine is contra-indicated in immune-compromised individuals and may elicit a suboptimal immunologic response. The aim of this study is to assess whether long-term immune responses against the YF vaccine are impaired in immune-compromised patients.

Fifteen patients using different immunosuppressive drugs and 30 healthy individuals vaccinated 0–22 years ago were included. The serological response was measured using the plaque reduction neutralization test (PRNT). CD8⁺ and CD4⁺ T-cell responses were measured following proliferation and re-stimulation with YFV peptide pools. Phenotypic characteristics and cytokine responses of CD8⁺ T-cells were determined using class I tetramers.

The geometric mean titre of neutralizing antibodies was not different between the groups (p = 0.77). The presence of YFV-specific CD4⁺ and CD8⁺ T-cell did not differ between patients and healthy individuals (15/15, 100.0% vs. 29/30, 96.7%, p = 0.475). Time since vaccination correlated negatively with the number of YFV-specific CD8⁺ T-cells (r = −0.66, p = 0.0045). Percentages of early-differentiated memory cells increased (r = 0.67, p = 0.017) over time.

These results imply that YF vaccination is effective despite certain immunosuppressive drug regimens. An early-differentiated memory-like phenotype persisted, which is associated with effective expansion upon re-encounter with antigen, suggesting a potent memory T-cell pool remains.