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This study examined changes in anti-Spike (anti-S) antibodies (Abs) and type I interferon (IFN-I) following the BNT162b2 vaccine in people living with HIV (PLWH) and analyzed the impact of demographic and immunological factors. In total, 75 PLWH and 28 healthy donors were followed at baseline (T0), at the second dose (T1), after the second dose (T2), and more than 1 year later (T3). Anti-S Abs were assessed by chemiluminescence and vesicular stomatitis virus (VSV)-based pseudo virus-neutralization assay, while IFN-α2, IFN-β, and IFN-ω mRNA levels were measured by RT-Real Time PCR. PLWH showed an increase in anti-S Immunoglobulin G (IgG) levels comparable to healthy donors (p < 0.001) and an induction of anti-S neutralizing Abs (p < 0.014 for T2 vs. T3). Age, gender, CD4⁺ T cell count, exposure to combined antiretroviral therapy (cART) and IFN-I levels at T0 did not affect the anti-S IgG production. IFN-I gene expression showed temporal changes, with a decrease at T2 (p < 0.01) and a subsequent increase at T3 (p < 0.001, for IFN-α2 and IFN-ω). A multivariable model revealed no overall change in the IFN-I response over time, except for IFN-β, which was lower at T3 than at T1 (p = 0.032). CD4⁺ T cell count was positively correlated with the IFN-I response (p < 0.05). These results suggest that mRNA vaccination can elicit an effective anti-S response and modulate the IFN-β gene expression in PLWH, with CD4⁺ T cell count being a key determinant of vaccine-induced changes in IFN.