Document resource
Background The ongoing mpox epidemic and the limited vaccine supply have raised concerns about the long-term effectiveness of the primary MVA-BN vaccination schedule. We evaluated humoral and T-cell immune responses up to three years after MVA-BN vaccination, according to prior smallpox immunisation.Methods Blood samples from individuals receiving a primary MVA-BN cycle (two doses for smallpox-naïve, one dose for previously vaccinated) were prospectively collected at each administration (T1 and/or T2) and at 1 (T2/T3), 6 (T4), 12 (T5), 24 (T6), and 36 (T7) months thereafter. Mpox virus-specific neutralising antibodies (nAbs) were measured by a 50% plaque reduction neutralisation test, and interferon-γ–producing MVA-BN–specific T cells by ELISpot. Statistical analyses included Kruskal–Wallis, Wilcoxon, and Mann–Whitney tests.Results We enrolled 102 men who have sex with men (MSM), median age 56.6 years (IQR 53.6–61.1) ( table 1); 6.7% had a history of childhood smallpox vaccination. Fifty-three (52%) were people living with HIV, mostly (83%) with CD4 > 500/mm3. IgG and nAb titres peaked one month after primary MVA-BN vaccination in both vaccine-naïve and previously smallpox-vaccinated participants. Thereafter, titers declined markedly in naïve individuals, with geometric mean titres falling below the detection threshold in most cases. In contrast, previously vaccinated participants maintained a robust humoral response (figure 1A-B).MVA-BN–specific T-cell responses followed a similar pattern in both groups: after the early rise, responses decreased substantially over time, starting to wane one year after the primary cycle up to the last timepoint, both in naïve and experienced groups (figure 1C). At three years, most participants were below the limit of detection (the median value detected in healthy donors).Conclusions Three years after primary MVA-BN vaccination, both humoral and cellular immunity waned substantially in smallpox-naïve individuals. In contrast, people with prior smallpox immunisation showed sustained antibody levels. T-cell response wanes in both groups. These findings suggest that smallpox-naïve populations may benefit from booster dosing to maintain long-term protection, whereas previously vaccinated individuals appear to preserve durable immunity.Abstract OC76 Table 1Characteristics of the study populationAbstract OC76 Figure 1Longitudinal evaluation of MPXV-specific IgG (A), neutralising antibodies (nAbs) (B) and MVA-BN T-cells specific response (C) in vaccine-naïve and experienced individuals three years after the primary cycle